Part of a continuing series of uncertain length on Tomes of Unspeakable Evil and the PCs who love them. So far I've blathered about how people get their hands on such books in the first place, and the effects of their dreadful contents on tiny human minds. But sometimes it's not about what you do to evil books, but about what the evil books do to you.
This was the stage where I got drawn into AncientHistory's thread that started all this waffling. They suggested that an evil book would need arcane abilities, so it wasn't merely a lump of paper vulnerable to all the usual things. The one that really struck me was the idea of a vampiric book that feeds on the reader. Cool. The book would draw power from its readers to fuel whatever abilities it had. AH didn't flesh out the mechanics much, but you could model this either as being solely reliant on readers to be anything more than a bundle of paper, or as providing extra power for the nastiest of its abilities while still being a dangerous occult entity at all times. I'll get into that later.
Call of Cthulhu
As we were talking Call of Cthulhu, there seemed to be several types of vampirism available. Each will play out in a different way during games, and they'll work differently depending on whether the book's intended for PC or NPC use, and what sort of timescale you expect it to operate on.
AH's suggestion was POW drain, which is immediately nasty: POW is a crucial resource for, primarily, not going mad, but also for resisting spells (or even casting them). A character drained of POW will get progressively more suggestible, more vulnerable to insanity, and eventually become a puppet of the book, I imagine. You could model POW drain either as an ongoing thing, with an absolute cap, or with a limited rate of drain. For long-term use, a cap would allow the book to be used by Investigators throughout a campaign without crippling them; on the other hand, the crippling bargain they strike with the tome could be a key aspect of the campaign. For a shorter plot, or if it's mostly used by NPCs, the book might drain POW more rapidly and quickly turn readers into mindless drones.
A character losing POW to a book is going to feel its effects immediately, and depending on the loss, it may be obvious to others as well. In metagame terms, it's also likely to alert the players that they're messing with something very nasty, for two reasons. One is simply that books don't usually cost POW, and you can't really reduce their stats without telling them (it's practically difficult even if they'd be okay with it).
I put forward two other options: Magic Point drain and SAN drain.
Magic Point drain
MPs are a very different kettle of fish, because you regenerate MP. MP drain is an insidious threat. It would depend on the rate of drain, but it's likely to manifest as unusual tiredness, with a risk of passing out during intensive reading. The reason it's more insidious is that it's a small and even negligible up-front cost, with little immediate impact on the reader's abilities. This means that in metagame terms, it's tempting to keep reading, to go and consult the evil tome just one more time because it'll make this investigation so much easier... a slow-drip bargain that allows the book to gradually build up considerable power, while each "transaction" doesn't feel like much of a price. It's also less obvious to players that something dangerous is happening, whereas having POW drained is the sort of thing that gets people's attention; and it's a marker of very sinister activities. It would be entirely feasible to keep the players ignorant of exactly what's happening, track the MP accumulation yourself, and just report any exhaustion or fainting to the players.
In character, the effects of the drain are much less obvious than POW, so even if players are aware, the characters could plausibly ignore what's going on until the book starts actually doing something with its accumulated power. It can prey on the same people for a long time, getting them used to 'bargaining' with it and feeding off their power to gradually achieve some plot or other, especially if you have a nice long campaign planned. Again, the seeming innocuousness of the drain could persuade characters to keep using the book even if they're aware of what's going on, because it doesn't necessarily feel like anything that bad is happening. Only when the book's accumulated a lot of power do they start to realise what a bad idea it's been.
Bizarrely, I'm inspired in this by Pontius Glaw from Warhammer 40,000 - a mad Chaos-worshipper whose imprisoned soul the protagonists become reliant on as a source of information, and by bargaining for each titbit, it gradually builds up enough resources to escape.
Feeding a book from the SAN cost it causes is more actively malevolent - the book feeds on the madness it creates, effectively. Though there are some similarities to POWvory, SANivory isn't likely to directly turn the readers into its servants, but simply drives them insane. It wants a constant source of new readers to torment, but once it's fed on them they're safe from further predations, at least in the normal rules. You could accept the initial 'price' but then the book would be effectively unable to feed on you any longer, and can be kept prisoner for consultation at your leisure. For a tome of immense power, that doesn't seem quite appropriate to me.
In this case, you might want to change the normal tome-reading rules. Perhaps it's so malevolent that each consultation costs a point of SAN even after the initial reading, just from forcing yourself to deny common sense and morality by reading the accursed thing. With this model, there's the slow drip-drip of power gained as in the MP approach, while players pay a cost that might seem low in the first place, but gradually builds up; and as their SAN drops they probably fall further under the book's influence. That doesn't necessarily mean becoming its servants, but it'd be natural for any insanities they accumulate to be vaguely aligned with the book's goals or contents.
You could also change the book's approach. Maybe it uses its power to ensure it passes from hand to hand, spreading madness and gaining power. This might be through mental manipulation, by creating cults that read it, or more directly by moving from library to library, either by physical movement or by 'possessing' other books. Again, I'll think about that later.
Of course, there's no reason a book needs to restrict itself to mental predations. Characters have a whole array of delicious stats to devour! A book might be able to feed on a range of them, perhaps for different purposes. If we're assigning the book some special abilities, rather than generic malevolence, then it might even gain stats by stealing them from others. These wouldn't tie into magic abilities in the way POW or MP might, but they're still fun.
An ancient tome might easily feast on the INT or EDU of readers to gain knowledge of the era around it. As readers find it increasingly difficult to reason and become forgetful, the book can exploit its new-found intellect to weave elaborate schemes. For an artful touch, perhaps the book actually gains new content as it feeds: previously-blank pages are gradually filled with shaky handwriting, or the book simply becomes fatter...
There's also the familiar idea of the occult scholar, pale and gaunt and over-aged from years of esoteric studies. Perhaps there's a more sinister reason for that physical condition than simple overwork and lack of sunlight. A book might feed, not only on mental energies, but on the very life of its readers.
If it drains CON from a victim, a book could become more resilient to all manner of damage (treating it as armour), or repair itself (think of The Mummy). Stolen STR might not be used in the same way as an animal would use it, but could allow it to exert physical force on the world - moving itself around, breaking out of locked cabinets, or used as part of a spell to attack, such as with telekinetic powers. DEX would help it to react quickly, and perhaps govern the manoeuvrability or speed of a flying book. APP is a natural way of making a book persuasive and domineering, increasing its influence over the weak-minded, and perhaps affecting the tone of its contents to be more appealing to readers.
Another arcane option would be for the Mythosier sort of TOUE to borrow, learn or even steal spells from a reader. In Cthulhu spells are a double-edged sword anyway, so working out how punishing those options are is going to depend on the situation and the spells in question. 'Borrowing' is probably more suitable to other systems, but a Cthulhu tome could easily acquire new spells from the brain of a reader. 'Learning' would mean simply gaining access to the spell, and perhaps adding it to its own contents. 'Stealing' would mean leaching it from the reader's brain entirely. Actually, this mechanism might be useful for non-TOUE artefacts, and could even be included as a fairly benevolent ability that helps protect people by trapping Mythos knowledge and cleansing minds of Mythos horror.
For any of these, the TOUE could simply gain the spell (or a random spell, or even all spells) automatically, or it could have to make its own spell-learning roll in the same was as Investigators do. There could also be an opposed roll to prevent the book from accessing the Investigator's arcane knowledge.
Outside Call of Cthulhu, similar policies would apply, tweaked for the stats in use.
D20 games are familiar with the idea of ability loss, though in D&D at least it's typically fairly easy to restore even 'permanent' drain with 4th-level spells. This makes the cost of consulting TOUE pretty negligible. As such, you might have to model this in a different way, perhaps having an opposed caster level check to overcome the book's baleful influence before the spells work.
Most of the stats in question would work the same way as in Cthulhu, though mental stats could pose extra complications because of their importance in spellcasting. This could make psychic vampirism a no-go because spellcasters would quickly lose access to higher-level spells.
One possible option would be to vary the book's effects based on the reader: a magically-inclined reader might learn valuable secrets from the mystical contents of the book, but find it physically draining; a warrior or rogue might find it mentally exhausting to read. You could also use the fatigue and exhaustion rules, though these are also easily negated, and some characters are immune anyway.
The D&D supplements Heroes of Horror and Ravenloft introduce some handy rules for Corruption (physical perversion), Depravity (mental perversion) and Madness (mental breakdown). Some combination of these could be used as an alternative way to model the effects of TOUE and similar influences in D20 systems, if you don't mind imposing some significant changes on the party. They could be reversible, if you're feeling kind. In the right game, certainly, players could have fun trying to conceal their claw-like hands, red eyes or twisted bones from NPCs. Or reigning in their behavioural issues.
These effects might be a long-term, slow-building consequence of constant exposure to the book, perhaps voluntary, and calling for significant roleplaying. Alternatively, they could be a fairly short-lived and pulpy issue if the book is more of a short-term plot element and you don't want to dwell too much on the Price of Power and all that jazz.
Skill points could also be at risk of vampirism. Maybe the book's own skills depend largely on its readers, and it can steal a point from a random skill each time it's read, adding it to its own skill. However, this kind of vampirism may be harder to explain and justify in-game ("I just... forgot how to pick locks?"), whereas sapping life force is pretty straightforward.
Spell vampirism I've touched on already. In systems with Vancian spellcasting, it'd be fairly simple to implement 'spell borrowing', where a book gains a single use of a spell from the reader. This might be a straight gain, or it might take that use from the reader, as though they'd cast it themselves. Spell learning is also pretty simple here, but spell theft would be trickier, especially for classes like sorcerers who can't freely learn new spells.
A similar process could be applied to more esoteric special abilities. Imagine that the book's simply absorbing knowledge and experience from its reader. Bard? Hey, it gained fascinate. Rogue? Oops, now you've got a malevolent book with +3d6 backstab damage. If you're feeling cruel, the book could steal an ability from each reader, and retain it until it's destroyed.
In a combat-oriented game where balance and stats are vital, and given the ease of overcoming most penalties, it might be easier not to apply the same kind of vampirism. Perhaps you simply add to a notional 'mana pool' whenever the book has the chance to affect someone.
In a similar way, you could tap other replenishable resources than Magic Points. These could include Hit Points - perhaps building up the book's own pool of health - as well as luck in games where it's a separate resource. But vampirism doesn't need to directly relate reader stats to book stats. A TOUE could perfectly well drain life energy and gain magic points, or turn any drained stat into a boost to any of its own stats.
Depending on the genre, the tone you're going for and the intended length of the TOUE plotline, you may want to have resistance rolls of some kind. If PCs have to regularly consult the book, and you're using a per-consultation drain, or if they slowly suffer effects as long as the book's in their possession, you could wear them out quickly. Also, it may be more interesting if some PCs are more vulnerable to the effects than others. On the other hand, if you're using one-off drains, this probably isn't necessary. For a short, snappy campaign, a heavier drain but with resistance rolls may be more appropriate to give it a dramatic edge.
Another possibility, slightly more arcane, is having the book exert a general 'baleful influence' that effectively produces bad luck. In some systems, there are actual Luck or Fate mechanics you could use: Cthulhu characters could suffer penalties to their Luck, Savage Worlds characters could lose bennies or have penalties to benny-based rolls, D&D has luck modifiers to die rolls. Rerolls might be limited or disallowed, or challenge thresholds increased. Die pools could be reduced whenever it seems appropriate.
Generally, I'd suggest that vampirism relate to the importance of the TOUE in the campaign, and potentially to the value of the book. It's going to depend on what sort of plot you're looking at, though. If the whole basis of the campaign is the existence of a dangerous vampiric tome, then it doesn't need to have much long-term benefit to readers, especially if it's in the hands of NPCs rather than PCs. Such a tome can simply be a baleful presence that saps the life and minds of those foolish enough to read it. On the other hand, if it's intended as a two-edged resource the PCs can use at a price, then there needs to be at least a belief on their part that it's worth keeping and reading.
So what do the effects of vampirism look like? This is important, particularly if players won't necessarily be aware of what's happening on a metagame level.
Again, how things get described will depend on what you're doing. If the book's nature is a mystery plot point, then you may not want to make the link between reading (or being near the book) and feeling strange very obvious. However, if it's supposed to be obvious, or the players are making costly trade-offs, then emphasising their condition is more important.
Various types of drain might end up displaying some of these effects:
- Feeling tired and short of breath
- Aching muscles, as though you've been doing physical labour
- Trembling hands, legs or eyelids
- Pins and needles, or numbness
- Headrush, dizziness or a sense of being off-balance
- Nausea, or gnawing hunger
- A heavy, leaden feeling to your movements, or clumsiness
- Weakness, or discomfort when doing physically-demanding things
- Loss of coordination, tendency to drop things, spill drinks
- Slow reactions, spacing out ('brown study')
- Headrush, dizziness or a sense of being off-balance
- Blurry vision, difficulty focusing
- Slow reactions
- Dry or flaking skin
- Low temperature
- High temperature
- Distractedness, sense of unease, lose train of thought
- Sensitivity to light or noise
- Regular 'tip-of-the-tongue' feeling when trying to think
- Indecisiveness, impulsiveness
- Feeling low, dull, uninspired or stupid
- Nervousness, loss of confidence, stumbling speech, embarrassment, self-consciousness
- Insensitivity, obliviousness
Luck is a bit more subtle and would need to be genre- and context-appropriate: in terms of descriptive effect, it could include finding hairs in your food, bumping into people while tracking a suspect, finding the lights always against you, pens running out or leaking, never having the right change, struggling to get a taxi or a room, or equipment malfunctioning.