Monitors: progress report and revisiting skills

Since I've now got 20 posts about this silly little project, and I'm wondering where to go next, let's quickly review what progress I have made.

1. Decided to try and actually make this into a game
2. Analysed reptilian biology for mechanics
3. Laid out some basic keystones for the game: skills-based, level-based, adventure-heroic
4. Roughed out skills
5. Roughed out races
6. Spent really an amazing amount of time on a body-temperature mechanic.
7. Established likely archetypes
8. Considered ways to make Monitors feel like part of a massive organisation
9. Spend a huge amount of time analysing and selecting basic principles for magic in the Monitors setting.

Well, considering I've never written an RPG before, that seems like actually a fair amount.

Revisiting Skills

The things I suggested looking at next are:

• Reviewing the skills/stats system in consideration of more recent posts
• Deciding on an injury system
• Thinking about tech
• Designing some basic spells and tech in light of mechanics
• Picking some numbers, however arbitrary, to use with said mechanics

On closer inspection, basically all of these boil down to "fixing the mechanics". This mostly means "fixing the skills", which were admittedly a stopgap measure.

The initial game mechanic ended up as a purely skill-based system where you roll under skill on a single die to succeed at tasks, with a block of 14 skills. There was no injury mechanic, and thus no discussion at all of things like combat.

It seems like I need to consider:

• The skills list: is it the right size, and the right breakdown?
• The mechanic: is a one-die roll-under system optimal?
• The skills system: would another system, such as stats-with-traits, be better?
• If, and how, skills and injury are to be linked.

Skills systems

At the moment, I have a fairly conservative list of 14 skills. This falls far short of substantial games like D&D (well, the editions with skills), Call of Cthulhu and so on, which means each skill is quite broad. However, it's still long enough that I can't readily use it with erosive damage, because a) tracking damage to 14 skills would get unwieldly very quickly, and b) the breakdown of skills doesn't really match up well to types of damage. It's not obvious what would damage Science, for example, and each skill mixes theory and practice. I also notice that none of them represents physical hardiness (though I could co-opt Strength). This all means an injury system is required.

Let's quickly see if there are any decent alternatives.

Stats and Traits

One obvious alternative to all this is an even more basic model (something Dan did mention). Drop skills entirely, and have a tiny pool of basic stats that's modified by fixed traits. This might look something like:

• Learning: how much information the character has memorised and can apply.
• Wits: how good the character is at analysing, resolving and reacting to situations.
• Muscle: how physically strong, fit and healthy the character is.
• Finesse: how good the character is at deft, fine movements, awareness of their movements and hand-eye coordination.
• Perception: how keen the character's senses are and how well they attend to them.

In this model, everything would simply be rolled against an appropriate stat. To represent specific training and racial qualities, characters would take traits, which might range from Chameleonic to Ferocious, and from Sneaky to Mechanic to Necromancer to 35th Century Betelgeusian Neo-Punk Enthusiast. A trait would help with a roll either by providing a bonus, allowing a re-roll or something similar. Maybe there'd be choices of Homeworld, Racial, Background and Personality traits to make.

In the simplest possible scheme, all stats might be rated 2-6 and you roll under them on a D6, with a relevant trait granting a reroll. Yes, I think roll-under is simpler than roll-over with fixed target numbers, because then your stats go up as they get better, which is generally more intuitive. A slightly more complex version would involve target numbers, and a stat + trait + roll system. Obviously you could faff about with this for a while (D10, percentage, what numbers to pick...).

This model would probably work okay with erosive damage, especially with fairly low stat numbers. Flash bombs damage Perception, alcohol damages Finesse and Wits, neuroscramblers damage Wits and Learning, tranqs damage Muscle and Finesse...

Well, it'd probably work. Running up a list of traits might be a pain though, and allowing people to devise their own is asking for balance problems. Still, could be worth a try.

Dice Mechanics

Not really my territory, so some mistakes are likely. But let's see, nevertheless. At the moment, I'm down as using a D20-based, roll-under-skill mechanic.

One incidental point is that I quite like the idea of allowing auto-fails and auto-successes, and am a lot less keen on the D&D-style "1 always fails, 20 always succeeds" model. In a fairly bouncy sort of game, it makes sense to me that some things just aren't a challenge to the skilled expert, and others are flat-out impossible. Criticals tend to lead to experts failing simple tasks 5% of the time, and amateurs succeeding at the toughest task 5% of the time. Obviously you can try to treat these as "complications" and other amelioratory measures, but I think it's simpler without them. In contrast, variable skills and difficulty modifiers seem to allow for fairly smooth transition between "impossible", "difficult", "normal", "easy" and "basically impossible to mess up". It just codifies the sort of DM judgement that normally happens: you have Skill 15, a +10 modifier for doing an Easy task that's easily repeatable with no risks, and you're rolling a D20 - just succeed already. But it might not work well in practice, of course.

What else is there?

Percentile Skill

One obvious change would be to just swap this for the good old percentile. In many ways this makes sense. People can intuitively handle percentages: your chances of succeeding at a task equal your skill.

One downside is that it seems percentile skill actually makes a lot less sense if you think about it a bit. Or rather, it still makes sense, but only if you bear firmly in mind that the only thing it represents is your chance of succeeding on a task of 'average difficulty', however that may be defined. However, it's very tempting to start using the character's skill to determine the difficulty of a task. Only got 10% in Mechanic? Well, then fixing this car will be Difficult for you (-5). Got 80% in Mechanic? You'll have no problem fixing this car, it's Dead Easy (+15).

This subjective evaluation isn't wrong, but it distorts the very intuitiveness that's one of the boons of percentile dice. Low skill and high skill are both inflated out of proportion.

Another slight difficulty is that, reasonably enough, the intuitiveness of the system also highlights its flaws. People want to be Good At Shooting, and (as any Call of Cthulhu forum can attest) find it frustrating if their skills are capped. "But I want to play a crack shot!", they think, "why can I only hit a target 80% of the time?" This is a justifiable concern, though the extent will vary between games; I think a lot of it comes down to the difficulty in pinpointing exactly what it is that you're 80% good at. Hitting a human-sized target? Hitting a stationary human in good lighting conditions? Landing an effective hit on a target during open combat, with smoke and noise and movement distracting you? How will the DM interpret it? What kind of bonuses and penalties are you likely to get? How does it work for other skills, like Interpretive Dance or Nuclear Physics? In this regard, weirdly, I think the abstractness of non-percentile systems actually helps, because they avoid this kind of deceptive intuitiveness.

A final point is that this is a fairly heroic game, where performing great feats should be fairly common. This suggests that very skilled people should succeed reliably even at difficult tasks (i.e. those with penalties) - which suggests skills high enough to overcome penalties. There's a natural resistance to allowing skills of 125%, which simply doesn't apply to having Skill 25.

Because of this complexity, I'm not sure it would end up an improvement over the d20 version I've suggested.

Difficulty Pool

Another variant, venturing closer into Dan's territory, is a version of the same thing using a pool of cumulative d10s. Yes, sounds weird, let me explain. Normally, you might roll 2d10 and aim to roll under your skill. For a very simple task, this might drop to 1d10. More difficult tasks would add dice instead. It would still be possible to succeed, but low rolls would become more extreme outliers with every die.

This system adds a bell-curve; you're more likely to roll a mean result (11) or close to it on 2d10 than on 1d20. The more dice added, the stronger the tendency becomes. However, on easy tasks with a single die, a lot of variation is possible. Is that a problem? Without doing some serious mathematical analysis I can't say for sure, and this isn't really the time. It's a possibility, though.

Dice Pool

Option three: give up and adopt a dice pool. As long as I pick and stick to one means of measuring success (that is, either numbers rolled or number of X-or-higher) and avoid the issues of Hellcats & Hockeysticks, it's probably fine. You get, say, 1-4 dice in some area of expertise, plus a trait may allow you a bonus die or a reroll. The main advantages here are that dice pools handle degrees of success quite neatly, it's easy to handle bonuses and penalties (just add or remove dice), and it's decent for a high-skilled setting because rolling a single 4+ on even 1d6 is pretty good odds.

On the downside, I think it actually makes it quite difficult to model the distinction between high-skilled PCs and low-skilled NPCs. You need a significant gap in their capabilities, which dice pools don't necessarily lend themselves to. If the lowest possible hand is one die, the dimmest bandit has a 50% chance of solving Fermat's last theorem (4+ on 1d6). If the lowest is zero, that chance drops from 50% to 0%, which is a pretty steep distinction and doesn't sit well with me. Also, we'd want to ensure that even a fresh Monitor recruit has a better shot at things than an untrained civilian.

You can shift the odds easily enough - maybe rolling a 10 on 1d10 is a success? - but the more you do that, the more dice you need when PCs come into question. In this regard, non-pool systems have an advantage because you can simply create a gap between the base PC and NPC numbers, and it's fairly simple to make this fine (percentile) or coarse (1d6) as you please.

Of course, there may be ways around this that I haven't spotted. I'm really not up on dicepool games. I could, of course, have NPCs simply work in a different way, but then I have to design two systems.

---

The TL;DR here is basically: I need to settle on a skill system. I'm dithering between "what I've got now, plus injury system" and "short stat-based system with stat damage, plus traits". The dice mechanics are important but secondary. Still honestly not that sure where to go next - perhaps drafting a version of each skill system to see how it'd work?

Monitors: making magic 8

So, designing some spells. Finally.

I'm not yet sure whether I want to go for off-the-peg or bespoke spells. At this stage, though, it's not all that important, since I'm just trying to invent some. So it doesn't really matter whether I end up with A Spell, or one spell from a set Lore, or one possible manifestation of a Lore.

According to me, I want magic to feel exotic, mysterious, significant, and maybe a little subversive.

Obligatory tangent

That Which We Call Summon Monster III

Okay, yes, I'm putting off design briefly yet again. A good starting point for feel is naming conventions: what you call something makes a difference to how it's perceived. "Golden Wind of the Lost Emperor" is good. "Proclamation of Gehazzural" is good. "Sigil of Burning Souls" is good. "Fireball" is not so hot. "Summon Monster III" is definitely out.

Portentous names help a lot in making spells sound dramtic. For now I'm going to assume a basic Noun Preposition Noun scheme, with optional adjectives. "Descent into Endless Winter" works, for example, as does "Anthem to Eternity".

Restrictions

Some spell types, like planar travel, curse removal or teleportation, are not really suitable for a system with limited spells. I would rather have these as plot-specific rituals or artefacts.

Actual spell design

So. What sort of spells do we want? Well, let's begin by cribbing freely from other games - I'm not going to actually import anything lock, stock and barrel, but the kinds of spells they offer will be helpful inspiration. Some spells will be the kinds of thing I want to include. Others will very much not be, and thinking about why should help me decide what it is I'm looking for.

Cribbing from Dungeons and Dragons

So I've gone through the spell lists for D&D SRD and picked out some example spells that made me think "yes", "no" and "hmm" to consider.

Verdict	Spell	Effect	Comments
Yes	Light	Object shines like a torch.	There are other ways to produce light, but it's a basic kind of spell
Yes	Hold Portal	Holds door shut.	Some form of seal seems good
Yes	Explosive Runes	Deals 6d6 damage when read.	Distinctly supernatural and full of character
Yes	Sepia Snake Sigil	Creates text symbol that immobilizes reader.	Distinctly supernatural and full of character
Yes	Sleet Storm	Hampers vision and movement.	Mechanics could be replicated, but it's a good magical effect
Yes	Black Tentacles	Tentacles grapple all within 20 ft. spread.	Nice weird effect
Yes	Crushing Despair	Subjects take -2 on attack rolls, damage rolls, saves, and checks.	Emotions are a good magical thing to effect
Yes	Hallucinatory Terrain	Makes one type of terrain appear like another (field into forest, or the like).	Some kind of illusion effect seems good
Yes	Entangle	Plants entangle everyone in 40-ft.-radius.	Mechanics could be replicated, but it's a good magical effect
Yes	Call Lightning	Calls down lightning bolts (3d6 per bolt) from sky.	Cool, obviously magical
Yes	Quench	Extinguishes nonmagical fires or one magic item.	Cool, obviously magical
Yes	Commune with Nature	Learn about terrain for 1 mile/level.	Very hard to replicate, a nice soft power
Yes	Wall of Thorns	Thorns damage anyone who tries to pass.	Nice weird effect
Yes	Meld into Stone	You and your gear merge with stone.	A nice strange non-attack ability that can't be replicated
Yes	Control Weather	Changes weather in local area.	Impossible to replicate, atmospheric, generally cool
Yes	Symbol of Sleep	Triggered rune puts nearby creatures into catatonic slumber.	Mind-affecting sigils are generally a good bet
Yes	Control Water	Raises or lowers bodies of water.	Impossible to replicate, cool, potential for interesting use
Yes	Insect Plague	Locust swarms attack creatures.	Just cool
Yes	Summon Monster I	Calls extraplanar creature to fight for you.	Can't be replicated; summons need careful thought but some kind of summons seems appropriate
Yes	Darkness	20-ft. radius of supernatural shadow.	Impossible to replicate, not an attack, cool, useful
Maybe	Blade Barrier	Wall of blades deals 1d6/level damage.	Can't really be replicated; perhaps too direct?
Maybe	Glyph of Warding, Greater	As glyph of warding, but up to 10d8 damage or 6th-level spell.	Dramatic, though it can be replicated by mines etc.
Maybe	Spike Stones	Creatures in area take 1d8 damage, may be slowed.	A good way to adapt the environment, can't be replicated, still works as an attack
Maybe	Chill Metal	Cold metal damages those who touch it.	Hard to replicate, interesting rather than powerful
Maybe	Warp Wood	Bends wood (shaft, handle, door, plank).	Hard to replicate, interesting rather than powerful
Maybe	Bestow Curse	-6 to an ability score; -4 on attack rolls, saves, and checks; or 50% chance of losing each action.
Maybe	Stone Shape	Sculpts stone into any shape.	A good way to adapt the environment, can't be replicated
Maybe	Break Enchantment	Frees subjects from enchantments, alterations, curses, and petrification.
Maybe	Mage’s Faithful Hound	Phantom dog can guard, attack.	Erm?
Maybe	Searing Light	Ray deals 1d8/two levels damage, more against undead.	Something that harms supernatural creatures is good, but this seems too weaponlike
Maybe	Wall of Stone	Creates a stone wall that can be shaped.	Transmuting the environment seems interesting, though I'm not sure about conjuring up things
Maybe	Passwall	Creates passage through wood or stone wall.	Transport spells are iffy, but this seems okay
Maybe	Chain Lightning	1d6/level damage; 1 secondary bolt/level each deals half damage.	Sorcerers are going to need some kind of actual attack
Maybe	Binding	Utilizes an array of techniques to imprison a creature.	Could be replicated, but a good classic kind of spell
Maybe	Antipathy	Object or location affected by spell repels certain creatures.	Nice and supernatural; too powerful?
Maybe	Silent Image	Creates minor illusion of your design.	Flexible, cool, fun,but could be replicated
Maybe	Obscuring Mist	Fog surrounds you.	Duplicates technology, like smoke bombs, but a version of this could be atmospheric and cool
Maybe	Hypnotism	Fascinates 2d4 HD of creatures.
Maybe	Cause Fear	One creature of 5 HD or less flees for 1d4 rounds.	Emotions again
Maybe	Enlarge Person	Humanoid creature doubles in size.	Impossible to replicate; definitely fun, but is it the right tone?
Maybe	Expeditious Retreat	Your speed increases by 30 ft.	Good bit of Bravestarr… too mechanical?
Maybe	Feather Fall	Objects or creatures fall slowly.	A bit niche.
Maybe	Resist Energy	Ignores first 10 (or more) points of damage/attack from specified energy type.	Overlaps with things like armour, but potentially good.
Maybe	Glitterdust	Blinds creatures, outlines invisible creatures.	Can be replicated, though it's interesting.
Maybe	Web	Fills 20-ft.-radius spread with sticky spiderwebs.	Hard to replicate, but possible; too D&D?
Maybe	Flaming Sphere	Creates rolling ball of fire, 2d6 damage, lasts 1 round/level.	Probably want this; it's a froody form of attack, not a substitute for a weapon, and just plain fun.
Maybe	Gust of Wind	Blows away or knocks down smaller creatures.	Can't really replicate it; a non-violent attack with other uses.
Maybe	Invisibility	Subject is invisible for 1 min./level or until it attacks.	Too powerful? I'm a bit hesitant about this kind of thing.
Maybe	Mirror Image	Creates decoy duplicates of you.	Nice and supernatural, though it's a D&D classic
Maybe	Alter Self	Assume form of a similar creature.	Could be replicated with tech, so is it worth it?
Maybe	Ghoul Touch	Paralyzes one subject, which exudes stench that makes those nearby sickened.	Could be replicated, but can be made properly weird
Maybe	Dispel Magic	Cancels magical spells and effects.	A form of antimagic magic seems useful, but I don't think a spell is the answer
Maybe	Clairaudience/Clairvoyance	Hear or see at a distance for 1 min./level.	Notoriously abused in D&D, but quite a good weird effect
Maybe	Wind Wall	Deflects arrows, smaller creatures, and gases.	That's just cool
Maybe	Feeblemind	Subject’s Int and Cha drop to 1.	A variant that's basically an attack might be okay, but I don't want save-or-suck effects
Maybe	Halt Undead	Immobilizes undead for 1 round/level.	Some variant could be okay, but this is too specific for my system
Maybe	Charm Monster	Makes monster believe it is your ally.	Can't be replicated, but I'm wary of mind-control stuff
Maybe	Water Breathing	Subjects can breathe underwater.	Easy to replicate, but still cool and useful; perhaps combine with some other underwater effects?
Maybe	Stoneskin	Ignore 10 points of damage per attack.	Narratively interesting, but duplicates armour
No	Mage Hand	5-pound telekinesis. (trivialises magic)	Trivialises magic, overly controlled
No	Endure Elements	Exist comfortably in hot or cold environments.	I'm wary of anything that interferes with body temperature mechanisms
No	Mage Armor	Gives subject +4 armor bonus.	Too mechanical
No	Darkvision	See 60 ft. in total darkness.	Tech easily replicates this
No	Blindness/Deafness	Makes subject blinded or deafened.	Tech easily replicates this
No	False Life	Gain 1d10 temporary hp +1/level (max +10).	Too mechanical
No	Spectral Hand	Creates disembodied glowing hand to deliver touch attacks.	Too gamey
No	Rope Trick	As many as eight creatures hide in extradimensional space.	Doesn't feel melodramatic enough; it's more fairy-tale or picaresque
No	Magic Weapon, Greater	+1/four levels (max +5)	Entirely mechanical
No	Secret Chest	Hides expensive chest on Ethereal Plane; you retrieve it at will.	This is for an utility-magic setting, not a weird-magic setting
No	Overland Flight	You fly at a speed of 40 ft. and can hustle over long distances.	Travel powers are a bit game-breaking, and we have tech for that stuff

Cribbing from Call of Cthulhu

A very high proportion of Call of Cthulhu spells fall into non-useful categories: they enchant items (crafting), summon deities (OP) or are fundamentally vile (inappropriate tone). Of the remainder, quite a lot are summon/bind varieties, and a significant chunk are extremely specific in both use and context. To a large extent these issues come down to COC's strong magic-is-wrong flavour, as well as the tendency to have specific spells for specific scenarios. However, I've found a few representative spells to consider.

Verdict	Spell	Effect	Comments
Yes	Red Sign of Shudde M’ell	Causes pain and death to those who see it	Creepy as anything, supernatural, can't be replicated
Yes	Command Animal	Allows limited control of an animal	Can't be replicated, interesting and fun
Yes	Candle Communication	Allows conversation through two candle flames	Semi-replicates tech, but in an interesting way
Yes	Unmask Demon	Reveals possessing spirits and the true nature of disguised creatures	Definitely fun, a classic magical feel
Yes	Summon X	Summons various monsters	Probably a better example of summons than the D&D ones TBH, with good limits and costs
Yes	Voorish Sign	Makes the invisible visible	Interesting, not overpowered and an alternative to tech
Yes	Parting Sands	Moves aside sand to clear areas or allow passage	Definitely fun, a classic magical feel, even though you can kind of replicate it
Maybe	Wave of Oblivion	Summons a tidal wave	Definitely supernatural, though overpowered
Maybe	Mindblast	Fills an enemy's mind with pain and horror	Needs some work, and seems a bit evil for PCs, but could be good in principle
No	Baneful Dust	Creates dust that damages supernatural creatures.	That's just crafting
No	Enchant X	Creates magical weapons and artefacts	That's just crafting

Cribbing from Deathwatch

Deathwatch spells are, fundamentally, combat spells. As such there's only a handful of examples I need give: while there are quite a lot of spells, most fall into a small number of categories, and quite a lot are just chapter-skinned versions of the same thing.

Verdict	Spell	Effect	Comments
Yes	The Avenger	Sends a flaming psychic projection to blast enemies	Needs tweaking, but has a nice narrative feel
Maybe	Truth Seeker	Makes the caster more aware of surroundings and details	Feels a bit mechanical TBH
No	Most other powers	Gives the caster a bonus to some stat	Purely mechanical
No	Gate	Creates a gateway between two places	Transport spells are just problematic to handle

Pattern recognition

Okay, what am I picking up here?

Good prospects

There's a definite "change" theme going on here. Quite a lot of the spells deal with transmuting or reshaping the environment in ways that aren't possible through any likely form of science. Water control, shaping terrain, clearing away the sand of aeons and so on.

Nature control is another theme that's going on, with several weather spells and some for manipulating plants, terrain or wildlife.

Wards, seals and repellents crop up several times, and these are good solid mystical things.

I've picked a few spells that conjure up effects or creatures. I think interesting things could be done with a selection of these, if chosen carefully. And it's really not something you can easily duplicate with tech.

Emotional and mind-affecting spells seem possible, and my concerns there aren't really thematic as much as mechanical, so let's assume some of those are going to be appropriate.

Ones to avoid

A lot of the spells I've disliked, and those I've reservations about, are quite mechanical in their effects. They tend to grant bonuses rather than having primarily narrative effects. Since there will be other ways to achieve bonuses, I don't really want spells whose main purpose is mechanical.

Similarly, there are a few spells (all in D&D) that are apparently built around the game mechanics, providing solutions to issues that arise from the game rather than to in-world problems: ways to deliver touch attacks at range, for example.

Another set of problems is utility spells. While these are quite fun, I'm not really looking for a feel where magic is used to get around mundane problems like storing equipment, navigating or providing mundane shelter. Even things like light spells seem over-simple and only replicate what can be done easily otherwise.

There's certain fun, quirky spells that don't quite fit the tone I'm going for.

Finally, I've taken against travel powers for a couple of reasons. A tech-heavy game pretty much has transport covered in everyday terms, so we don't need to worry about getting around in general. Powers that allow even short-range teleportation and flight massively distort the expectations of a game, by removing barriers. It's obviously possible to deal with that, but I don't particularly want to remove the game that far from normality and from adventure-story conventions. Serious transportation magic - that is, as character spells rather than restrictive rituals or fixed portals - completely changes and often breaks games. It allows scry-and-die tactics, massively reduces the possibility of interesting journeys, breaks most scenarios designed around isolation, causes problems with imprisonment and infiltration missions, and so on and so forth. At this point heavy-handed countermeasures tend to be needed and the whole thing turns into a mess.

Tentative spellmaking

Okay, enough excuses. I'm going to make a spell or two. Obviously this will be pretty rough to due lack of solid game mechanics.

I currently see three broad categories of spell. Instantaneous spells will take effect and then end. Concentration spells will continue as long as the wizard can devote some attention to them: they may end when the wizard falls unconscious, or when something else distracts the wizard, such as casting another spell or engaging in combat. Persistent spells will simply continue until their ending conditions are met.

Wizards are unaffected by their own spells except where it suits them. I haven't yet decided how likely allies are to be affected; this is a bit of a tone issue.

Onslaught of Wrathful Winds

A howling wind erupts behind the wizard, rushing in whatever direction they desire. Nearby creatures must battle against the wind or be slowed, dragged along or hurled off their feet. Small objects are blown around, and dust or other debris may choke and blind those affected. This spell may stir or quench fires, drive away gases, ward against flames or sprays of liquid, and so on. It can counter the effects of existing winds.

This spell can be maintained by concentration. It does not work in confined spaces, nor in a vacuum.

Unchaining of the Wild

Vegetation erupts into furious growth, ensnaring creatures and enveloping structures in an area. Creatures may be trapped by the tangling plants, and objects or mechanisms immobilised. Under appropriate circumstances, the plants may hold together damaged buildings, cushion falls, slow down speeding objects, reduce visibility and so on.

This spell has a range. It does not create plants from nothing, and its effect will vary with the quantity and nature of local vegetation.

Invocation of Primal Nightmares

Utter dread erupts in the mind of nearby creatures, their worst ancestral fears overwhelming them. Those unable to choke down their fear may freeze, flee, scream or otherwise react appropriately.

Mindless entities are unaffected by this spell.

Emerald Sigil of Splendour

The wizard draws a glorious symbol in lines of burning green, drawing the eyes of onlookers and transfixing their minds. Creatures able to see the symbol must test each turn or stand transfixed in admiration.

This spell can be maintained by concentration. Mindless entities are unaffected by this spell.

At this point, I realise that I'm going to have to revisit stats and skills as there's nothing obvious to test against.

Covenant with Night

Pure darkness roils through the air, blotting out sight and warmth alike. No light from infra-red to ultraviolet can penetrate it, and creatures within are blinded. Navigation by sound and touch is possible. Other electromagnetic wavelengths, including radio, gamma and X-rays, can penetrate it. The darkness does not cause cooling, but blocks most sources of heat.

This spell has a range and persists.

Call the Ashen Beast

Dust and smoke coalesce into a grey, predatory form. The beast is an elemental that defends the wizard, obeying simple commands. When the spell ends, the beast disperses into lifeless dust.

This spell persists.

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From here on, I can't really make much progress without firming up mechanics. I think the main things to do are:

• Reviewing the skills/stats system in consideration of more recent posts
• Deciding on an injury system
• Thinking about tech
• Designing some basic spells and tech in light of mechanics
• Picking some numbers, however arbitrary, to use with said mechanics

Monitors: making magic 7

So, decision time. Before trying to design any spells or anything, I'm going to pick at least some placeholder systems for How Stuff Works.

Theory

Bits of magic

As discussed in part 2, magic is going to be split into several distinct areas of talent.

1. Academic knowledge of things magical and supernatural will be handled by the Occult skill. This will also probably cover interacting with magical artefacts or existing spells, and performing generic rituals.
2. Actual spellcasting prowess is established during character design.
3. As things currently stand, there's no hard difference in magical strength; spells are powered by expending heat points. I could tie this into a skill, but frankly I don't see any reason to. If traits are introduced later, I suppose there might be a trait for enhanced spell power.
4. I'm not planning an actual crafting system; magic isn't tame enough to be making magic swords and stuff all the time. Any plot-specific crafting needed will be handled by rituals or via NPCs.
5. Use of simple artefacts will be handled with appropriate skills: Firearms for lightning wands, for example.

What magic is like

As discussed in part 3, magic is there to do what technology doesn't allow. It bends time, alters weather, instils emotions, conjures things from thin air, curses and petrifies. Where technology is quantitative, magic is qualitative.

Spellcasting will have side-effects. As I want magic to be used fairly readily, but not ubiquitous, the side effects need to be relatively minor, but with potential to cause interesting complications. Because this isn't a "magic is evil and self-destructive" setting, they should not directly imperil the caster or their allies, nor should the side effects themselves be horrific. My initial thought here is some kind of chart, where you'd roll a die plus the power of the spell to determine the category of side-effect, then roll up a side-effect.

Casting is (at least initially) going to be reliable. One reason is that it has a cost and side effects, so unreliability on top of that seems likely to discourage spellcasting, where I want it to be fairly frequent. Another reason is that it's hard to portray a wizard if your spells never work. Again, I might tinker with this later on (perhaps there's a small failure chance, perhaps more powerful spells are unreliable...) but for now any unreliability will come effect rolls, not from failed casting.

Characters

As discussed in part 4, I'm going to start by giving all PCs of the same 'level' the same amount of spellcasting ability, which is to say the same amount of spells (whatever 'spells' may be). Later I might experiment with giving limited flexibility to trade this off against other benefits, but as a starting point this is definitely way simpler.

Spellcasting will be powered on a depletion system based on body temperature. By and large, this means Monitors (and other reptiles) are far more magically-competent than others. However, this will not be the only cost, as side-effects must also be considered.

Monitors: making magic 6

So I've pretty much done the analysing and theorising (slash pontificating) side of things, and I really need to just actually, you know, design a magic system.

I wasn't even going to get into powering spells until after I'd done most of the other stuff, but an exciting idea turned up in a chat with Dan, who calmly said something like "why don't you just tie spellcasting into body temperature?" as if it wasn't some kind of stroke of genius. I think it may be, actually. If it works out, this could well handle a whole slew of things all at once, as a side effect of powering spellcasting.

Endothermic Magic

So, spells drain body heat from you to provide their power; or at least, as a consequence of casting you get colder. One obvious consequence of this is that it provides a casting limit. You can only cast spells while you're warm, and either caution or sheer physics will limit what you can do, due to unwanted falling unconscious.

One really nice thing is that it gives a big boost in importance to the temperature management system, which is great because I'm keen for that to be a meaningful part of the game, especially since it's a unique feature. It also makes it more interesting, because now rather than just temperature, there's an interplay of factors to think about.

Of course, if you're in a room above freezing, then technically you're going to be able to cast unlimited spells given enough time. This is only really an issue if heat transfer is rapid and spellcasting is rapid. Otherwise, we can just trust that it won't really be that beneficial compared with other things you could do in that time. If cooling down is a serious problem, and warming up takes a while, then trying to exploit this becomes worthless. Not that I particularly expect people to be breaking Monitors, but I don't want to design in flaws unnecessarily.

On the other hand, if you're in a hot room, then casting spells will actually enable you to cool down. This is potentially quite a cool (no pun intended) mechanism, and I quite like the idea of overheated lizards grimly chanting away in a desperate attempt to stay conscious by channeling unstable arcane energies.

Details

There's obviously details that need fiddling with. How many therms can you spend on a spell, or within a single round? Having characters drop their body temperature by thirty degrees in a few seconds seems a bit extreme, but you could allow use of powerful spells by spending therms over a number of rounds. This would provide a way to limit more powerful spells, by imposing a logical time-cost, as well as potentially allowing for very powerful rituals where heat sources are required over long periods. I'm inclined to say one or two therms per round would be as much as you could reasonably spend, unless I wanted to introduce rules for risky overspending.

An important note: if I use this system, I need to prevent using magic to restore body heat, otherwise we're getting into limitless magic territory by accident, while pretending not to be there. That's not going to work out well.

Mammals and spellcasting

Another vital issue is the effect of endothermic spellcasting on non-poikilotherms. One simple option would be to translate therms directly into damage, which is likely how I'd deal with environmental heat and cold. This would handily boost the setting's herpetocentricism by providing another mechanical reason why reptiles are Better At Stuff: they can handle magic much better than mammals because they can withstand its physiological effects more readily, and this once again means they're a good option for special response teams.

Mammals would still be able to cast spells, but in most cases their capacity is much more limited by the pain incurred through spellcasting. Some non-reptiles would also have magical capabilities (fish, some insects, some aliens), and might have variable heat capacities in the same way as the reptiles.

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So basically, this seems like it would usefully:

• Provide a mechanic for powering spells and limiting spellcasting
• Provide a mechanical cost to spellcasting
• Provide a fluff sense of cost to spellcasting
• Reinforce the narrative favouring of reptiles in the setting
• Increase mechanical differentiation between poiks and non-poiks (and degrees of poiks)
• Increase the mechanical importance of temperature regulation
• Improve integration of temperature regulation with other mechanics

What's not to like?

Conversions: Horrors of Tzeentch for D&D

So I appear to be converting Warhammer-mythos creatures for Dungeons and Dragons. Right. Okay.

This idea was partly inspired by unearthing an old article on the Icosahedrophilia blog, and partly by my long-standing interest in mashing up D&D and Warhammer lore; in this case, the wild and bizarre Chaos creatures of the Warhammer universe.

Some Chaos critters are pretty straightforward, things like Bloodletters for example. I'm going to start by taking a look at one of the more interesting ones, the Horrors of Tzeentch.

Horrors of Tzeentch by Curtis

Horrors of Tzeentch for 3.5

Horrors are knobbly warp-spawned creatures with vaguely orangutan proportions, except that they skip the body bit entirely, connecting their toothy maws directly to stumpy legs and enormous arms. Their fingers end in a mixture of claws or gecko-like suckers, and their skin is covered in protrusions. Horrors babble constantly to themselves, producing a distracting chatter infused with a touch of arcane power that plagues the minds of mortals - basically like the typical "hearing voices" scene in films. pink horrors are savage but jubilant, cackling gleefully and whooping as they wreak havoc. When a pink horror is injured, though, its skin stretches and bursts apart, and two small blue horrors erupt from the remains like insects bursting from a cocoon. These are bitter, squabbling creatures, but no less dangerous for it; they bicker constantly, but their focus is still on maiming mortals rather than fighting amongst themelves. Only when the blue horrors are vanquished is the demon finally destroyed. As well as their physical brawn, as servants of the Lord of Change and magic, horrors have magical prowess. The amount varies a fair bit between editions of Warhammer and bits of lore.

Statswise, horrors are tough creatures rather than terrifying monsters. They're scary enough to devour civilians, but for veteran soldiers it's hordes of the things they have to worry about. They're very communal, and their magic is implied to be a collective rather than an individual thing. Taking a look at demons in D&D 3.5, there are a few wimpy ones around CR1-2, but the majority seem to push into CR10+. However, things like achaierai, abishai, advespas and so on hover around the 3-5 mark, which I think is roughly what I'm looking for. These should be horde monsters that will rampage through militia, can be fought off by hardened veterans (your level 3-4 warriors) given good odds or preparation, and which experienced adventurers can hack apart with a bit of effort. I suppose I'm looking for a feel that a horde twice the size of the party is a challenge and three or four times the size is a serious threat.

The signature move of horrors - bursting apart into smaller horrors - complicates the balance. This effectively provides additional HP to the monster, as well as a measure of protection from one-hit kills. Also, the ability to produce more (if weaker) creatures needs considering in terms of attack capacity. As such, horrors need to be somewhat less immediately threatening than their challenge rating suggests.

Another problem is that demons in Warhammer tend to have a collective magic thing going on. Basically, as creatures of the Warp, they are made of the stuff of magic, and the more demons in an area, the greater their magical power becomes. This works fine in a tabletop wargame, where the maths balances out fairly well, but I'm concerned about translating it to an RPG where Challenge Rating is pretty crucial. If you think about it, the difference between five CR4 creatures who can cast flaming hands at will and ten CR4 creatures who can cast burning hands at will plus fireball once each per day is enormous. To look at ways to handle this, I've looked at kuo-toa clerics and the shocker lizard, both of which have similar abilities.

In Warhammer, horrors may use several different powers; depending on the edition, that might be down to unit size, a random die roll during setup, or a straight-up purchase. Some of these are great for battles, but problematic for RPGs - for example, bolt of change transforms a victim into a rampaging chaos spawn, which is too much for a low-level monster, let alone the problem of every single horror having this power. In the end I decided that firestorm of Tzeentch is the emblematic horror power: not only is it one of the powers actually available to them, but it also summons additional horrors from the souls of the slain.

Another complication is that the way horrors work in Warhammer has actually changed a fair bit over various editions of the rules. Sometimes they're basically tenacious monsters, sometimes they're gibbering hordes with some magical power who can replenish their ranks by transforming enemies, and in the most recent rules I've actually seen, they're actually ranged specialists. But to my mind that's just not that interesting.

Finally, there are a couple of points where the blue horrors' attributes end up slightly out of whack with CR, notably their spell resistance and the DC for their cackling ability. This is very simply to keep things simple, so that players confronting a mass of pink and blue horrors have only a single SR and a single DC to deal with. I felt like the streamlining was worth the discrepancy. Moreover, blue horrors are intended only to show up as the spawn of pinks, and so designing them as a fully-balanced independent creature just isn't that important to me.

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Oh, this seems like a necessary starting point: a new subtype. While there's no particular canonical reason for the miscellaneous resistances, they're cribbed right off existing demons. The transmutation resistance just seemed thematically appropriate, though it doesn't have any firm basis in Warhams.

Tzeentchian subtype: demons of Tzeentch share the following properties:

• Damage reduction 5/silver or lawful
• Darkvision 60 ft.
• Immunity to fire and poison
• Can choose to ignore any transmutation effect that would alter their form.
• Resistance to acid and electricity

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Pink Horror of Tzeentch

This brilliant creature has no body, merely a wide-mouthed face atop two stumpy limbs. Its apelike arms gesture constantly as it cheers and grins, the irregular fingers tipped randomly with claws or suckers. A faint corona of many-hued light flickers over it, leaving a whirling radiance in its wake.

Horrors of Tzeentch are bizarrely misproportioned servants of the Lord of Change. Pink horrors are born from raw chaotic energy, and their forms vary wildly. They are insanely cheerful, and maintain a constant babble of gleeful malice. They are constantly in motion, bounding and leaping, sometimes on all fours, scrambling over and across obstacles with their muscular arms, and rending their victims with savage talons.

The magical power of the horrors grows as they congregate, allowing them to conjure up storms of chaos-flame that warp and twist their victims. As entities of living chaos, they are extremely resistant to alteration themselves, but revel in changing others.

When a pink horror is finally struck down - or simply chooses to spawn - its body writhes as two blue horrors wriggle out, leaving only a shrivelled skin. No-one can tell how these creatures form, or which of the two is their natural state. The smaller blue horrors are as morose and bitter as the pink are jubilant, dextrous and frail where the pink are lumbering. Though less powerful than the pink horrors, the sheer numbers of the blue make them a dangerous enemy. Eventually, two blue horrors will coalesce into pink horror, though often in a new combination as a new entity. Such is the nature of the Changer of Ways.

Size/Type:	Medium Outsider (evil, extraplanar, chaotic, tzeentchian)
Hit Dice:	5d8+10 (32 hp)
Initiative:	+2
Speed:	40 ft. (8 squares)
Armor Class:	16 (+2 Dex, +4 natural), touch 12, flat-footed 14
Base Attack/Grapple:	+7/+7
Attack:	Slam +7 melee (1d6+2)
Full Attack:	2 slams +7 melee (1d6+2) and bite (1d6+2)
Space/Reach:	5 ft./10 ft.
Special Attacks:	Cacophonous cackling
Special Qualities:	Damage reduction 5/silver or lawful, darkvision 60 ft., firestorm of Tzeentch, fission, immunity to fire and poison, luminous, resistance to acid 10 and electricity 10, spawn of change, spell resistance 15.
Saves:	Fort +6, Ref +5, Will +5
Abilities:	Str 15, Dex 14, Con 14, Int 9, Wis 13, Cha 12
Skills:
Feats:	Improved Grapple, Power Attack
Environment:	The Warp
Organization:	Pack (5-8), mob (12-20), horde (30-80)
Challenge Rating:	4
Treasure:	None
Alignment:	Always chaotic evil
Advancement:	6-10 HD (Medium)
Level Adjustment:	—

A pink horror's natural weapons, as well as any weapons it wields, are treated as evil-aligned and chaotic-aligned for the purpose of overcoming damage reduction.

Fission (Ex): A pink horror reduced to zero hit points collapses. On its subsequent initiative count, two blue horrors burst out of its body, leaving only shreds of rubbery skin. The blue horrors take their sire's initiative count and can act immediately. The condition of the pink horror's corpse is irrelevant; if necessary they will clamber out of split halves, emerge from pools of molten demon-flesh, or coalesce from shredded fragments. A pink horror slain by other means or banished does not undergo fission.

Cacophonous Cackling (Su): The constant jeering, whooping and chattering of pink horrors is highly unnerving and interlaced with arcane energies. This is a free action continued every round. All creatures other than worshippers of Tzeentch within 20 feet of the horror must succeed on a DC 13 Will save or become shaken until 1d3 minutes after they escape the noise. A creature that successfully saves cannot be affected by the cackling for 24 hours. This is a sonic mind-affecting compulsion effect. The save DC is Charisma-based.

Firestorm of Tzeentch (Su): Two or more pink horrors can combine their innate arcane energies to unleash a storm of sorcerous fire once every 1d6 rounds. The pink horrors must join hands to focus their magic, but need merely remain within 30 feet of one another while it builds. The firestorm affects a 30ft. radius within 100ft. and line of sight of at least one pink horror. All creatures within the blast suffer 1d4 damage per contributing horror: half of this is fire damage, the other half results directly from diabolical power and is not subject to fire resistance. In addition, the magical energies warp the target's body chaotically for 1d6 rounds, imposing a -2 penalty on attack and damage rolls, skill checks and saving throws until they stabilise. A successful Reflex save will halve the damage and limit the warping to a single round. Tzeentchian creatures are unaffected by this ability.

If a creature of 4 or more hit dice is slain by the firestorm, a pink horror manifests within 5 feet of the victim.

Spawn of Change (Ex): Pink horrors can choose to ignore any effect that would alter their form, including any consequences of such a change. This includes polymorph effects, size changes and physical distortions.

Luminous (Ex): Pink horrors exude constant neon-pink light in a 5' radius.

Blue Horror of Tzeentch

Size/Type:	Small outsider (evil, extraplanar, chaotic, tzeentchian)
Hit Dice:	2d8 (9 hp)
Initiative:	+3
Speed:	40 ft. (8 squares)
Armor Class:	16 (+3 Dex, +2 natural, +1 size), touch 14, flat-footed 10
Base Attack/Grapple:	+3/-1
Attack:	Slam +3 melee (1d4)
Full Attack:	2 slams +3 melee (1d4) and bite (1d4)
Space/Reach:	5 ft./5 ft.
Special Attacks:	Cacophonous cackling
Special Qualities:	Damage reduction 5/silver or lawful, darkvision 60 ft., firestorm of Tzeentch, immunity to fire and poison, resistance to acid 5 and electricity 5, spawn of change, spell resistance 15.
Saves:	Fort +3, Ref +6, Will +4
Abilities:	Str 11, Dex 16, Con 10, Int 9, Wis 13, Cha 12
Skills:
Feats:	Weapon Finesse
Environment:	The Warp
Organization:	Found only with pink horrors.
Challenge Rating:	2
Treasure:	None
Alignment:	Always chaotic evil
Advancement:	3-4 HD (Small)
Level Adjustment:	—

A blue horror's natural weapons, as well as any weapons it wields, are treated as evil-aligned and chaotic-aligned for the purpose of overcoming damage reduction.

Cacophonous Cackling (Su): The constant grumbling, snarking and chattering of blue horrors is highly unnerving and interlaced with arcane energies. This is a free action continued every round. All creatures other than worshippers of Tzeentch within 20 feet of the horror must succeed on a DC 13 Will save or become shaken until 1d3 minutes after they escape the noise. A creature that successfully saves cannot be affected by the cackling for 24 hours. This is a sonic mind-affecting compulsion effect. The save DC is Charisma-based.

Firestorm of Tzeentch (Su): Blue horrors cannot conjure a firestorm of Tzeentch, but can contribute to one conjured by pink horrors. Every two blue horrors participating increase the damage dealt by 1d4.

Spawn of Change (Ex): Blue horrors can choose to ignore any effect that would alter their shape, including any consequences of such a change. This includes polymorph effects, size changes and physical distortions.

Luminous (Ex): Blue horrors exude constant electric-blue light in a 5' radius.

Horrors for 4E

To some extent 4E actually makes things easier, because the monster-building is more... organised. There's less fiddly bits to consider, the system has some built-in utilities like "activate on death" powers, and I can just basically assign whatever abilities I want.

On the downside, you now have to allocate things like roles, which I frankly can't guess. They're kind of big and gangly mobs, so maybe soldier? But the Warhammer writeups don't really justify them having great defences. On the other hand, they're clearly not brutes because they don't hit hard (although they can soak damage), and they're not lurkers or controllers. Let's just go with skirmishers. The firestorm of Tzeentch is a bit of an issue, but let's not worry about it for now.

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Pink Horror of Tzeentch	Level 5 Skirmisher
Medium immortal humanoid (demon, chaotic)		XP 200
Initiative +4	Senses Perception +4; darkvision
HP 40; Bloodied 20; see also fission
AC 19; Fortitude 17, Reflex 15, Will 18
Speed 5
Immune fire, polymorph; Resist 5 force
Traits
Cacophonous Cackle (sonic, charm) ♦ Aura 3
Attack: +9 vs. Will
Hit: the target incurs a -2 penalty to attack rolls and skill checks until the start of their next turn.
Luminous
A pink horror exudes neon-pink light, illuminating all adjacent squares and making it visible in darkness.
Standard Actions
(M) Claw ♦ At-will
Attack: +9 vs. AC
Hit: 1d8 + 4 damage
RB Firestorm of Tzeentch (fire, radiant) ♦ Recharge 6
Attack: Area burst 2 within 10; +8 vs. Reflex.
Hit: enemies within the burst suffer 2d8+2 fire and radiant damage. If a target is reduced to 0 hit points or fewer, a blue horror spawns within the burst area.
Triggered Actions
Fission ♦ Encounter
Trigger: when reduced to 0 hit points.
Effect: the pink horror is replaced by two blue horrors. The blue horrors retain their sire's initiative count.
Horde Arcana ♦ At-will
Trigger: an ally within 4 squares uses firestorm of Tzeentch.
Effect (Immediate Reaction): expend a charged firestorm of Tzeentch to grant +1 to the ally's attack rolls and increase the damage inflicted by 1d8. Using this ability does not count as an attack or provoke attacks of opportunity.
Skills Arcana +9, Athletics +8,
Str 18 (+3)	Dex 15 (+2)	Wis 12 (+1)
Con 12 (+1)	Int 13 (+1)	Cha 11 (+0)
Alignment Chaotic evil	Languages Abyssal

Blue Horror of Tzeentch	Level 3 Minion Skirmisher
Small immortal humanoid (demon, chaotic)		XP 38
Initiative +4	Senses Perception +2; darkvision
HP 1; a missed attack never damages a minion.
AC 16; Fortitude 14, Reflex 12, Will 15
Speed 6
Immune fire, polymorph; Resist 5 force
Traits
Cacophonous Cackle (sonic, charm) ♦ Aura 3
Attack: +9 vs. Will
Hit: the target incurs a -2 penalty to attack rolls and skill checks until the start of their next turn.
Luminous
A blue horror exudes electric-blue light, illuminating all adjacent squares and making it visible in darkness.
Standard Actions
(M) Claw ♦ At-will
Attack: +9 vs. AC
Hit: 5 damage
Triggered Actions
Horde Arcana ♦ At-will
Trigger: an ally within 4 squares uses firestorm of Tzeentch.
Effect (Immediate Reaction): any damage inflicted increases by +1. Using this ability does not count as an attack or provoke attacks of opportunity.
Skills Arcana +7, Athletics +6,
Str 13 (+1)	Dex 16 (+3)	Wis 12 (+1)
Con 12 (+1)	Int 13 (+1)	Cha 11 (+0)
Alignment Chaotic evil	Languages Abyssal

In this case, I departed somewhat from the original horrors, trying to keep within 4E tendencies. Rather than the miscellaneous resistances of the 3.5 horrors, I picked out two thematically-appropriate ones: fire because of their abilities and the association of Tzeentch with fire, and force because it's the closest to raw magic the game gets, and Tzeentch is very much the magic one.

For the cackling, I was torn between an aura and a minor action attack. In the end I went with an aura because attacking only a single creature seemed inappropriate, and because it's just supposed to be something that happens from being around them. However, this does mean a single horror affects all nearby enemies.

The firestorm power is much easier than in 3.5, because triggered actions are a great way to model contributions to other people's powers. It also allows pink and blue horrors to contribute different amounts nicely. On the downside, it's basically impossible to model the slow build of the power across a unit. I was very tempted to make it an encounter power that begins play uncharged, in order to prevent unscrupulous DMs unleashing a whole horde's powers at once, but I'm not keen to introduce unnecessary exceptions. It's quite hard to judge the effect of cumulative damage. I hope that the balance of the firestorm's damage, recharging and horde arcana will work out well. Horrors must choose between using their own power and enhancing another horror's attack, and this also provides a way for blue horrors to contribute in a minor way. I knocked the damage down to below the usual amount for a limited damage at 5th level, in order to allow for both recharge possibilities and cumulative damage; in theory you could end up with a gang dealing 7-8d8 damage even so, but only once, and that's still only 36 damage - not enough to take down a single 5th-level character. Sounds about right. It's possible that this is actually underpowered, but I think it's about right when recharging is taken into account.

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So anyway, hope that was fun for someone. I might do more in future, but we'll have to see.

Monitors: making magic 5

In this seemingly-endless set of posts about magic (currently including how other people do it, what magic means in game terms, approaches to what magic does, and ways of allocating magical power), there's still at least one thing I'd like to consider, which is different ways of casting spells.

A lot of this will involve theorising about the flavour particular approaches will produce, which I haven't actually tested. So take it with a pinch of salt; I cheerfully acknowledge it's just musing.

Bespoke and off-the-peg magic

In terms of actual spells, there are two main approaches.

Off-the-peg

Off-the-peg magic is the one I'm most familiar with, as used in Dungeons and Dragons, Call of Cthulhu, Deathwatch, Dying Earth and many many others. Here, all spells are predefined by the designers, and casters simply select (or generate randomly, or inherit through background) from the lists. They may be able to choose spells at the time of casting, or may have to pre-select them to various levels of strictness (once, daily, etc.).

Advantages of this system:

• The spells that exist are known during design, and balance or gameplay issues can be worked out.
• Specific spells can be explained clearly and coherently. Their capabilities, limits and situational uses can be laid out in one place.
• Limits can be placed on particular uses of specific spells that might create gameplay issues.
• Players can see what effects are possible, and choose from a list that has been balanced and themed. While applications of spells may vary, analysis paralysis should be limited.
• Individual spells can be themed for the game, helping to produce the desired tone and genre.
• Spells can be made highly individual and esoteric, giving a sense of very arcane magic.
• Spells can be heavily tailored to particular classes, backgrounds, monsters or individuals, reinforcing their nature.

Disadvantages of this system:

• Individual spells often take up large chunks of rulebook.
• Every spell needs careful balancing and testing, to avoid must-haves and nevers.
• Casters need to pick specific spells and plan characters around their options. This is particularly true of (D&D) wizard-type systems that restrict known spells, vs. cleric-type systems where casters know all spells they're eligible for.
• Games can be clogged with variations on a theme.
• Games can be clogged with level-varied versions of the same spell - sometimes even though each one also scales with level. D&D features this with whatever summoning XXI-type spells.
• You may end up with several spells that do specific but similar things, rather than one more general spell. This might be to block an exploitative option that exists between the intended ones.
• In real play, there will always be unexpected synergies, situational uses and 'exploits' not spotted by designers, so the system cannot totally prevent this.
• A small group of designers will never be as inventive as the sum of all players, nor predict the questions and situations that will crop up. By limiting spell use to a set of preconceived options, they may restrict in-game creativity (though there's always creative use of existing spells).
• Combinations of spells need analysis to make sure broken combinations don't appear by accident.

Bespoke magic

In contrast, this system is based on a small number of flexible parts, which can be controlled or combined to produce specific effects. Ars Magica combines verbs and nouns of various disciplines to allow spell creation on the fly, for example. In a more school-based version, a caster may have the ability to Summon Elementals, or Telekinesis, or Electricity, and perform various feats within that discipline depending on personal ability and intention.

Advantages of this system:

• Allows wide scope for creativity.
• No long lists of specific spells clogging up the rulebook.
• Variation around a theme and level-scaling can be handled automatically, without the need for repetition of similar spells.
• Gives a feel of creative, imaginative magic and mastery of magical forces.
• Casters have a great deal of flexibility, with no need to plan spells beforehand. This avoids the problem of little-used niche spells in off-the-peg systems.
• System has potential to be mechanically very simple.
• Magic is intuitive, fluid and subject to the caster's imagination, giving a sense of understood or perhaps innate power.
• Disciplines and their combinations can be themed for the game, helping to produce the desired tone and genre.

Disadvantages of this system:

• New spells can always be created, so testing and predicting possibilities is difficult.
• It may be difficult to coherently explain the limitations and possibilities of magic when it has no set spells. This can venture into confusing territory with hypotheticals, exceptions and conditions all over the place. Information can't easily be bundled into relevant packages, but is likely to be spread out.
• For rulebooks etc., spells must be invented whenever examples are needed.
• It will be tempting to fall back on the same old spells (or the 'best builds' dreamed up by players), reducing the advantage of creativity.
• The capabilities of the characters are hard to predict, since much relies on the players' creativity. They may not think of possibilities envisioned by the scenario writer or GM.
• Some uses of a discipline may end up under-powered, and others over-powered, because they are not individually tweaked.
• The range of options available may cause choice paralysis, particularly if powers can be combined freely.
• With spell design in the hands of players, 'spells' as used may not fit the intended feel.
• Expanding the range of disciplines calls for reanalysis of everything, in case broken synergies are introduced.

Mana, mana, tekel upharsim

The next question is how spells and caster are powered. There are a number of common systems for fuelling spells. These relate to background, the genre and assumptions of the game, and balance.

Mana pool

In this system, characters have a pool of resource points specifically for casting spells (though it might be shared with other supernatural abilities, such as ki powers). This includes Call of Cthulhu Magic Points.

This system gives characters flexibility in spellcasting, and makes magical effort like physical effort: you can do a few major things or many small things before being exhausted. It places a cap on the amount of spells the character can cast in a given interval, useful if you want limited magic. Mana can also allow flexibility in the power of individual spells, if casters can spend more mana to enhance spells.

Mana systems can be combined with a casting roll; you might pay a fixed cost and roll, or bet a number of mana points that determines your likelihood of success. This is good if you want uncertainty, and the feeling that spells are costly and unreliable. The second option introduces tension and choice, and allows for both desperate long-shots and absolute determination to succeed. A disadvantage here is that a mana cost, plus a casting roll, plus any rolls for effect, may feel like just too many hoops to jump through.

Mana systems may also be used to avoid explicit level-limitations on spells. If the mana cost is too high, it's impossible for a low-level caster to use Spell of Utter Destruction. Conversely, in a betting system, even an apprentice wizard can have a shot at Spell of Utter Destruction, but their odds increase with experience.

Vancian magic

In this system, individual spells are prepared in advance and expended when used. It's generally a case of memorising and forgetting spells, but it could also be skinned as actually casting a spell beforehand, and then using a brief incantation to trigger the final stage - that's how I tend to rationalise it myself.

This system emphasises the importance of individual spells, and makes predicting upcoming challenges a key part of playing a caster. Both obtaining suitable spells to memorise, and choosing appropriately, are crucial. It automatically limits what casters can accomplish in any day, and does so more strictly than any other method - it's easier to grant extra mana to a caster than explain why they suddenly remembered a spell in defiance of normal magical law, and why that spell in particular.

An obvious limitation is, this is mostly suited to off-the-peg magic. I suppose in theory you could devise and prepare spells in advance, but the 'study and memorise' aspect of Vancian magic really clashes with the freeform creativity of bespoke magic. It also tends to sideline niche spells, since it's rarely worth preparing one on the remote chance it's incredibly useful, when you could prepare a common spell that'll almost certainly be quite useful.

As a pseudo-Vancian model, you could have casters choose disciplines in advance; this works for me to some extent with clerics, who might pray for particular kinds of blessings (protection, strength of purpose, strength of body) and then determine their manifestations as necessary. In a setting with varying sources of magic to tap, such as elements, a caster might have to actively replenish their power by tapping one or more, and their choices would determine what kinds of disciplines they could use that day. Of course, this partially offsets the benefits of flexible casting, but it might make for interesting play.

Spell slots

In this system, casters have 'slots' of varying level that can be used to cast spells, but can choose which spell to cast as and when. This is the sorcerer model from D&D.

The system grants greater flexibility than Vancian casting, since spells don't have to be prepared beforehand. This makes being a caster less of an odds-juggling role, and removes the possibility that a suboptimal spell choice will cripple you until the next rest. It makes it more likely that niche spells will be cast at all. At the same time, it keeps a mixture of weak and strong spells going, and provides a way to neatly scale caster power with level - just provide new spell slots.

If you want to encourage (well, force) casters to cast a lot of minor spells, a few substantial ones and just the occasional game-changer, this is the model. It prevents them from burning up their arcane power on a couple of ultra-spells and then having nothing to do. On the downside, it removes the option to do exactly that. Back on the upside, given players' prediliction for demanding to rest as soon as the wizard's out of spells, that may not be such a bad thing. But you could introduce other limits (some form of exhaustion, say) to prevent over-spend in other systems.

Some systems let you spend a slot of a different level to produce more or less powerful versions of a spell.

This model can work with either bespoke or OTP magic, as long as there's a way to determine the slot a spell should fit.

One significant disadvantage is that while the model's simple, it's also very artificial. Spell slots don't correspond to anything intuitive (though it's possible to construct settings where they work), and you can end up with the situation where a wizard is only able to cast very powerful spells, having exhausted low-level slots already.

Skill roll

In this system, casting a spell is basically like any other action: you roll against a target number. There is no other limit on casting, but there may be side-effects of both failure and success. This is the system used in Warhammer 40,000 RPGs.

A skill roll system may have a strict threshold, but often the roll determines the effectiveness of the spell, with very good rolls producing a particularly effective casting. Skill rolls dependent on level, or on stats that vary with level, are good for soft scaling, since higher-level characters will find it easier to cast spells and will do so more effectively.

The inherent unpredictability of skill-roll systems gives an unreliable feel to magic, and this is often supplemented in practice with mishaps and brilliant successes, which allow for occasional flashes of brilliance and for horrible side-effects. It's ideal for settings where magic is inherently dangerous or chaotic (cf. Warhammer 40,000). However, that doesn't have to be the case; it can also represent magic as simply difficult to do. Depending on the distribution of casting rolls, all spells might be very difficult to use, or some may be effortless and others challenging. It's a very flexible system; on the downside, the maths needs careful consideration to produce the desired effect. You need to decide what target numbers are needed, how they'll be affected by levelling or stat variance, and whether the ease of casting across the whole range of spells still matches your intention at various different levels.

Another decision to bear in mind is how many rolls are called for. If there's a casting roll for spells, then designers need to decide whether you also need to roll to hit targets, to overcome wills and so on.

Despite the unpredictability, this system gives a lot of power to casters, since the issue is not usually whether they are capable of casting a spell, but whether their odds of success are good enough. Given enough time, they can generally succeed - assuming that any consequences of failure aren't too catastrophic. This means mishap charts and the like are a very strong influence on the feel of the game: without them magic is merely challenging, but a mishap chart's tone can flavour magic anywhere from 'hilarious' to 'frustrating' to 'psychotically dangerous'. There's also the question of whether mishaps affect only the caster (which makes it their call), or spill over to influence other allies and enemies (which makes them a collective issue, and can make casters a liability).

Unlimited casting

Does exactly what it says on the tin. I can't immediately think of anything that allows this fully, but some recent D&D-type games allow unlimited use of certain minor spells.

Logically speaking, there's no particular reason why spellcasting has to be limited when (say) punching people in the head or swimming across rivers isn't. You could use the same system to handle both, whether that's a cheerful "no limitations", or some kind of exhaustion system. If necessary, powerful spells could be limited in the same way that other powerful abilities often are, through resource requirements: missile launchers need missiles, fireballs need bat guano. This would introduce a dichotomy between self-powered spells (the equivalent of physical and mental feats) and magical techniques that require special equipment or supplies (the equivalent of technical feats).

Of course, unlimited casting isn't necessarily cost free; you could perfectly well combine it with a random effects table, so that the decision becomes a cost-benefit analysis. Is it worth risking conjuring a flock of noisy crows as I magic a hole in the castle wall? Or putting everyone to sleep by casting a lightning bolt?

Fundamentally this is going to give a very accessible feel to magic, whether that's the controlled feel of mishapless magic, a chaotic wellspring ridden with unpredictability, or a dangerous but tempting force that's all too easy to tap into.

Depletion

This system draws on the caster's physical resources to power spells. Effectively, casting spells does damage to the caster.

I'm sure this is used somewhere (I can't imagine I'm the first person to invent it), but I don't have any actual examples.

This seems like it would work best in HP-type injury models, where depletion can be predicted and managed. A system with injury charts would make spellcasting very dramatic, but I feel like it would tend to be too dangerous to actually use magic (or at least, feel that way) if there's a good chance of blinding yourself or rupturing your spleen. Of course, in a system designed for painful choices and self-sacrifice, that might be fine, and the extent of injuries could be limited.

Rather than depleting an HP pool, the other option is depletion of stats. Depletion could affect a 'casting stat' (as the brain's magic centres get tired), or drain physical strength. It could even stack up, applying general penalties to various actions, as a form of exhaustion.

This approach seems like it would make magic seem exhausting and personally costly to use, but relatively predictable. Even a random injury roll is more controlled than magical mishap charts - you might break a leg, but you're not going to create a rain of frogs or reverse gravity.

Randomness

So you've got a way to define spells, and a way to power them. But how reliable are they?

Randomness is going to be a significant influence in terms of tone. A non-random magic system will make magic predictable, reliable and relatively straightforward - it's a tool that can be called on, providing you can meet the requirements and pay the price. In contrast, a highly random system makes magic unreliable, unpredictable and potentially risky (randomness may or may not include outright danger).

I've covered a lot of this above, but the main types of randomness are casting reliability (will I get this spell off?) and side effects (what else might happen?).

Casting reliability

Casting reliability partly determines the position of casters. Are they masters of arcane energy, or just dabblers? Can they summon up the power when it's needed, or is it always a gamble? The less reliable casting is, the more amateurish casters are likely to seem. It's hard to maintain the 'wise, powerful wizard' schtick if you're failing multiple spell attempts in quick succession. Unreliable casting is good for things like Cthulhu where magic is a mysterious force and PCs are bumbling amateurs dabbling in What Man Was Not Meant To Wot, but bad for Dungeons and Dragons.

Side effects

Side effects, in contrast, are all about the flavour of magic. The choice of whether they're automatic, rare, or a consequence of failure will make a lot of difference: the first makes magic seem chaotic, the second gives a complex and mysterious vibe, and the third makes it technically tricky and risky.

The type of side effects is likely to be a big factor in establishing genre, though I reckon what you don't include is maybe more significant than what you do. Warhammer 40,000 features casters floating into the air and ignominiously falling back down, and accidentally summoning demons, both of which could equally well feature in a slapstick game. However, it doesn't have rains of custard, people transforming into animals, silly voices, and other silly elements; the overall balance of effects maintains the sinister and untrustworthy nature of magic.

Of course, Warhammer 40,000 mixes things up by letting casters decide how forcefully to unleash their powers, and adjusting the chance of side effects accordingly. This helps the tone quite nicely: you can focus your efforts on keeping the spell under strict control at the cost of reduced effort, or you can summon up all the power at your command, exposing you to the dangers of the Warp.

Arguably, 'critical casting' (in some incarnations) can be a form of side effect, with the spell far more effective than expected (potentially creating its own problems). The disparity emphasises lack of control over the power you unleash.

The other facet of side effects is how serious they are. Minor side effects will tend to give an esoteric feel, without substantially affecting gameplay. Major side effects can seriously disrupt plans, threaten characters and generally chance the balance of the game. In the middle you have effects that cause inconvenience (or unexpectedly help out), being about as effective as a player action or two, but aren't likely to ruin things. The more serious the side effects, the more of a chancy proposition magic becomes: the stakes are higher, and it's often going to be wiser not to take the risk. So if you want magic to be heavily used, and you're not running a game where with hilarious consequences is a common theme, I suspect side effects should generally be smaller.

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Okay, we're reaching the point where I can't tell if I'm making sense any more, so let's call it there.