It's true that Call of Cthulhu doesn’t have the same monster balance situation as games with more of a PC power scale in them, like D&D or GURPS or Vampire or whatever. Monsters aren't a tactical challenge, but typically a narrative one, to be overcome by intellect or endured, rather than defeated. So you're not looking for a monster that provides a particular combat role and has a particular mathematical power relationship to PCs. At the same time, PCs don't level, so their power level compared to the monsters doesn't change much, except through changes in equipment or acquisition of a vital spell.
On the other hand, I think you can make a reasonable argument that monster balance is an issue you need to consider in scenario design. Monsters are extremely powerful in Call of Cthulhu, and most of them are perfectly capable of a TPK. In fact, forget monsters – an ordinary human is a serious threat to the party, in a game where a single lucky headbutt can kill. To take an ridiculous example, when you're picking something to scare the party outside the antagonist's lair and prove her sinister connections, but which they can overcome and proceed to a confrontation (or just blow the place up) you want to pick a ghoul rather than Great Cthulhu. Similarly, if you're looking for a terrifying abomination that needs to be evaded until they can escape or find a cunning solution, a ghoul just isn't tough enough to cut it (unless they're unarmed kids, for example).
However, I agree that it’s not the same kind of balance. You’re not weighing up Challenge Ratings or build points, and the power of monsters can be pretty difficult to establish. Also, you’re not just trying to create combat challenges of various levels for the party, but a whole range of possible interactions, with direct combat just one option.
Very broadly speaking, I think the balance issue for Call of Cthulhu is not “how powerful is this monster compared to the party?” but “how will this creature interact with the party?”. Different kinds of capabilities are appropriate for different cases. Sometimes you do, in fact, want something that will wipe the floor with a whole army. Sometimes you want something a single human can realistically defeat, or maybe outsmart. Sometimes you want something that doesn’t do combat at all: a psychic parasite, a malevolent presence, a predator on the vulnerable. And sometimes, you do want an interesting fight. Obviously, the balance of those will vary between groups, play styles and campaigns. The suitability of any monster for a particular role depends on a lot of different criteria.
Job-seeking for monsters
For example, ghouls tend to get on with their own business, which occasionally intersects with living humans. If discovered, they might take measures to eliminate witnesses, but might also try to recruit them, strike a deal, or even leave them be if they don’t consider the person a threat. They don’t tend to hunt humans or actively meddle in human affairs, but might do so if they want to track down a particular treasure, or as part of an overall goal, such as dealing with a rival Mythos entity, or protecting an important location. An individual ghoul is only slightly more dangerous than a human, and a party can reasonably expect to survive an encounter with one. Of course, a ghoul is intelligent enough to avoid direct conflict if they don’t expect to win. However, where there’s one ghoul, there are probably more to come.
Ghouls are good for things lurking in shadows up to mischief, which can be beaten or driven off in small numbers, but who need to be defeated for good by stopping whatever plot they’re up to, which doesn’t necessarily mean direct conflict. They’re good as monsters that a party can tool up for and then confront directly. They’re also good as grey-area entities, who might have to be bargained with. They know all kinds of things, and are relatively relaxed about sharing them. They have understandable motivations and personalities, however twisted. However, a ghoul is not a particularly good fit for a single monster lurking at the evil heart of the town, because most are not very powerful or even that imposing. They’re not suitable as a terrifying entity that should send people (especially Investigators) fleeing in dread, or a Big Bad that’s intended to wreak havoc on the party; at least not as written.
...of a gigantic hound!
A hound of Tindalos, on the other hand, is a lone predator. It will relentlessly hunt down its chosen prey, taking delight in the fear of its victim. Its actions are restricted by a different and alien set of physical laws. It does not, in the usual way, deal or bargain, and can’t be scared off by pretty much anything humans can achieve. It’s vastly more powerful than a human, and immune to all but the most powerful of attacks; actually bringing any of those to bear on a teleporting time-traveller is yet another problem.
A hound is a great monster if you need a terrifying hunter, something that has picked off other victims regardless of protection, and now it’s after *you*. It’s a good motivator to get people moving, or doing frantic research, or taking desperate and possibly abhorrent measures to protect themselves – maybe go and make a deal with those ghouls. On the other hand, it’s not a good fit for a surprise to spring on the players, because an unexpected hound is a TPK by another name. As written, it’s not particularly good as the single evil heart, because it’s not the scheming manipulative sort and doesn’t tend to have followers. If you want something skulking about that the players might ambush and defeat as their first real evidence of Mythos involvement, a hound is far too dangerous. If you want a sort of haunted house mystery, with a creature lurking in the shadows that will strike at them, but eventually be defeated, a hound is possible, but problematic.
The Young Ones
Dark young of Shub-Niggurath are servitors, and immensely powerful ones. They have an array of magical powers, are incredibly strong, and terrifyingly resilient. They tend to either lurk in the wilds for their own mysterious purposes, or serve as focal points for cult worship.
A dark young is ideal as the great lurking evil that investigators must hunt down, and even better as the great evil that they must discover and then escape from. As the immediate centre of a cult, it’s much better than ghouls or hounds. They’re also decent as things to lurk around, motivations unknown, but clearly too dangerous to confront. On the other hand, a dark young is not so good as a hunter-down, since they’re big and obvious and it’s hard to have them skulking around. They’re not great as a gatekeeper monster for investigators to defeat or drive off during an investigation, or as a warning shot sent by some cult or sorcerer (while you could send a dark young just as a scare tactic, nobody insane enough to summon one is likely to try and restrain the thing). It’s possible to defeat one, but in planning a scenario that would be a big assumption to make unless you plan the setup to give investigators plenty of tools and options.
Okay, that seems like enough.
So when you’re planning a scenario, it’s reasonable to worry about whether a particular monster can fill a particular role in the game without either a) getting mown down in a hail of Fist/Punches and tommy-gun fire; or more likely b) wipe out the entire party when you didn’t want it to. There’s always going to be some margin of error, and you can make ad-hoc adjustments to some extent, but you want to gauge things at least roughly.
Monster analysis for fun and profit
Here’s a few things I might consider when looking at monsters. Obviously, a lot of these you can simply change, to fit your own interpretation of a monster or your own requirements. You can make it act more or less intelligently, and people often ignore the possibility of monsters having spells.
- Some are roughly comparable to a human, with similar endurance and physical strength.
- A very high proportion have tough hide, alien anatomy or are immaterial, and so are very difficult to damage.
- Some are very strong, and can easily fend off a human or rip one apart.
- Some have acidic blood, poisonous breath or consist of energy, and so approaching one at all is dangerous to humans.
- Consider their skill percentages for attacks. These can make a major difference in the deadliness of an enemy.
Movement and speed
- Some can’t move
- Some are slow and sluggish
- Some are fast and quick to react
- Some can fly
- Some can burrow
- Some can teleport (or switch between clone-bodies at will, or leap to a new psychic host...)
- Some creatures have powerful supernatural attacks or spells. These can easily allow them to injure or kill investigators.
- Some creatures can enslave, terrify or otherwise control investigators, which alters the balance of power, and denies investigators the full use of their capabilities.
- Some creatures can summon other creatures to reinforce them, or to hunt down investigators.
- Some creatures can magically escape from difficult situations, so are very difficult to destroy or defeat permanently.
- Some creatures can haunt dreams, track down individuals’ psyches, and otherwise cause harm from a distance.
- Is it a mindless thing that acts purely on sensory input? These can be outwitted and manipulated by clever investigators.
- Is it a beast, acting on instinct from hunger, fear, pain or rage? Investigators can plan how to deal with these, and predict their behaviour to some extent.
- Is it somewhat intelligent, capable of rudimentary planning, setting ambushes, manipulating its environment, and predicting human behaviour? These can spring surprises on investigators, especially if nobody knows about them.
- Is it of human intelligence, able to scheme, deceive, manipulate, build, destroy, use and learn with the best of them? These are exactly as dangerous as humans, pretty much.
- Is it superhumanly intelligent? This one is (naturally) very difficult to model, except in terms of technology and learning capability. Naturally, these are extremely dangerous to deal with, because investigators can’t even rely on their wits to overcome a more powerful entity.
Behaviour and attitude
- Randomly preys on people wherever it likes, so isn't a persistent threat but a constant menace.
- Actively hunts down specific targets, under its own motivation or under orders, which leaves those targets in permanent danger but others largely safe.
- Attacks intruders on its territory, but doesn't hunt, so it's relatively easily avoided.
- Stays in one place unless disturbed, then defends itself and may become more active; not provoking it is the best course of action, at least in the short term
- Exerts a malign influence through dreams, disease, spores, catalysing weird events... this creature's very existence causes problems for humans, and it needs to be escaped, destroyed, banished or otherwise dealt with to shake off those influences.
- Captures victims for later consumption or experimentation, which means there's some chance of escape, but the creature is a long-term threat and may have horrific aims.
- Captures victims and physically enslaves them, so escape is possible, and captives could be freed. The creature needs them for a purpose, so what is that purpose?
- Captures victims and transforms them into minions; they may be savable from mental domination, but not physical transformation. Such creatures present a lurking threat - are people who they seem, or minions of the enemy?
Just how unsettling is the creature to see? Some are mildly repellent, others horrific and disturbing. Some force you to rethink your concept of reality. A creature with low SAN loss (anything up to a 1d6) is easier to shrug off narratively, and to pass off as something else - an ugly thug, a mask, a wild animal. Mechanically, it's unlikely to impose an insanity unless it's the latest in a string of shocks. A creature with high SAN loss is much more mechanically dangerous, because it's far more likely to cause an insanity that may prevent an Investigator from reacting appropriately. This means they may struggle to survive a threat that they could normally escape or deal with. This is more of a concern in groups that roll for insanities, as a Keeper can always select something that won't be crippling.
So I'm going to take a quick look at roles that monsters (and non-monsters) might take on in a Call of Cthulhu game. These are somewhat different from things like D&D roles, because they're primarily narrative rather than tactical. This is really off the top of my head, so feel free to disagree. Another point is that monsters may take a very different role when facing a party of armed soldiers, compared to a group of foppish professors; roles are always relative to the protagonist. Similarly, the tools offered by the scenario make a major difference: heavy weaponry, magical artefacts or spells can turn lethal opponents into only moderate threats.
Cultist: lackeys of a primary antagonist that work towards its aims. They are not initially easy to distinguish as monsters, so betrayals may occur. Cultists may be actual cultists, hypnotised minions, parasite hosts, human-looking monsters and so on. They normally occur in groups. Cultists are typically about as dangerous as humans, so one or two can be beaten by a party, half-a-dozen need careful handling, and larger groups present increasingly overwhelming threats. The party's technological capabilities, especial weaponry, usually make a significant difference to their chances against cultists.
Hordling: a creature that turns out to exist in significant numbers. Individual hordlings are, at most, slightly more dangerous than a human (though without weapons that's of little consolation). However, killing just one achieves little. Typically protagonists find themselves amongst hordlings, seeking a way to escape without being caught by the creatures; they may be actively hunted, or simply in hiding. Occasionally protagonists actively venture amongst them to retrieve a friend or item, either by stealth or in disguise. Hordlings may be able to adopt humanoid guise, or may be actually human. The Shadow over Innsmouth is a fine example of hordling monsters.
Gatekeeper: a creature that is overcome (one way or another) in order to continue with the scenario. A gatekeeper may provide final confirmation of the main antagonist's evil, perhaps being the first real proof of supernatural or monstrous presence in the story. Gatekeepers may be anticipated or unexpected; sometimes they are encountered early in a scenario but can't be defeated at the time. They are typically alone. They are threatening, and may have some immunities, but can be defeated with concerted effort from the protagonists. Physical force is often enough to defeat them.
Messenger: a creature that typically serves as a weapon of the true antagonist. It is sent to assassinate, kidnap, torment or warn off potential threats, either as a one-off or as a regular tactic. A messenger is often enslaved by the antagonist, but may also be a loyal servant, powerful hireling or the Brawn half of a dual antagonist. Messengers are quite dangerous, but tend to stick to their specific purpose, which means they won't bother to kill people who aren't in their way. They also often have a decent sense of self-preservation, and will back off if exposure or serious harm threatens. Because entertainment, fear or deterrence is often their goal, they don't mind letting victims escape and won't hunt them down relentlessly. A messenger is typically much more powerful than any individual protagonist, and sometimes more powerful than the party as a whole, but can be evaded or defeated with cunning. Messengers are often immune to some kinds of attack, but have specific weaknesses that can be exploited. Releasing a messenger from its servitude (or banishing it) may be a good solution. Defeating the messenger is not required to complete the scenario, but may be possible.
Beast: a creature that is the primary antagonist of a scenario, and protagonists are expected to defeat it as the climax of the adventure. It is typically a single creature, occasionally a small group. The beast is very powerful, and presents a major threat to the party obliged to deal with it. Defeat may mean destroying the creature in pitched battle, luring it into a trap, discovering and performing a ritual to banish it, or breaking its hold on a victim (especially a possessor or parasite). Monsters like a lone werewolf or Predator are classic beasts.
Hunter: a creature that is a major (often the primary) threat in a scenario, and which the protagonists must escape. It may be a relentless hunter that pursues them across space and/or time, and needs to be deterred or banished. Alternatively, protagonists may be trapped with the hunter, for example on a wooded island or in a spaceship, and need to physically escape. A hunter may be destroyed in a scenario, but this happens offscreen: the reactor core overloads, the ritual takes effect, the forest burns with the creature inside. Alternatively, the cavalry may capture or destroy it with resources far beyond those of the protagonists. Destruction is usually open to some question (and the possibility of an implausible sequel). Several apparent defeats may occur during a scenario, with the creature returning each time, perhaps regenerating or possessing a new body.
Final Horror: a vast, monstrous evil that is uncovered. A final horror is far too vast and monstrous to be destroyed, and sometimes has no physical form to attack; it can only be escaped, and often not even that. Anyone trying to fight a final horror is doomed. Most people encountering one are also doomed. Cthulhu himself is a good example.
Analysing the Fire Vampire
For example, let’s look at the fire vampire. It’s not especially physically imposing, to be honest, but you can’t exactly brawl with it, so that doesn’t help. On the other hand, you can use normal physical obstacles against it, except that it can fly. It’s fast and manoeuvrable. It’s very difficult to harm by normal means, but vulnerable to things that extinguish flame – in theory, if you locked it in an airtight room, it’d burn out eventually. What mainly tips the balance is its fire attacks, which can cause an awful lot of damage to investigators in a pretty short time. While some weapons inflict similar damage, the resilience of the fire vampire tips the balance: it can damage investigators much more easily than they can damage it.
So in terms of direct confrontation, a fire vampire is a tough proposition for Investigators. It’s going to work well as an assassin, since it can fly, it’s fairly discreet, and its attacks can even be made to look like a normal fire. By giving the Investigators some heads-up, though, you can also use it effectively as a guardian of some location or artefact, which they must prepare to defeat. They’re good as roving monsters, visible from a distance and quite scary, which investigators must evade as they explore or escape some area – sure, you can destroy one with luck, but it’s risky and you’ll probably just attract more attention. You could probably use a fire vampire as a beast, actually: it’s dangerous and resilient enough that investigators will struggle to defeat one unless they’re prepared for the fight.
As a cultist, the fire vampire is clearly no use. You could potentially use one as a hordling with the right setup: scientists in a facilty might end up playing cat-and-mouse with an invasion of fire vampires, sneaking around the base and occasionally destroying one with a fire extinguisher.
Fire vampires make effective messengers: they're powerful enough to wreak havoc, and hard to kill without the right preparations. Their fiery nature means they can't easily capture or retrieve, but as assassins or warnings (or indeed, for destroying evidence) they're great. They're very often summoned as servitors, and are surprisingly discreet in many ways, so don't draw too much attention.
A fire vampire might serve as a gatekeeper. It's not a great match, especially because it relies mostly on ranged attacks that make it relatively hard to defeat. However, a messenger fire vamp might turn into a gatekeeper if tracked back to a lair of some kind; perhaps a crucial room in a sorcerer's home. Overall, though, I feel they don't quite have the right character to be a good gatekeeper. They're not quite alive enough, and too good at following people and hunting them down.
As a hunter, the fire vampire is good in many ways, but too vulnerable to mundane attacks to have the required staying power. It might work somewhere that didn't provide access to water or sand; simply boosting its hit points might do the trick, but once you start modifying creatures it's a new calculation. With a slightly different balance of power, a fire vampire could also be an effective beast, since it's dangerous and defeatable. Its manoeuvrability and insubstantial nature may cause some problems, though. You really want both beasts and hunters to be more like a powerful predator, limited by the environment and somewhat predictable, so that protagonists can escape from it and cower in fear somewhere.
Finally, without some serious modification, a fire vampire is not really suitable as a final horror. For one very important thing, it's not nearly big enough or monstrous enough, being just a little ball of fire, which isn't especially horrifying or sanity-blasting. Mechanically, it's not powerful enough to be an utterly overwhelming threat to a party of adult humans, since some lucky work with dust, water or even some fireproof blankets can take one out.
Right, I think that's more than enough uninformed wittering from me.