GURPSよろず

　In a horror campaign, the GM may wish to make some or all supernatural powers inherently evil. The Black Magic rules in GURPS Magic provide one way of handling this for magic. Other options include the power tally used by ThresholdLimited Magic and the Spiritual Distortion of Assisting Spirits, both in 『GURPS Thaumatology』, and the point-debt model of Meditative Magic in 『GURPS Fantasy』 – all of which could be interpreted as buildups of corrupting influences that might eventually lead the mage to develop “evil disadvantages” like Callous and Sadism. These approaches to the Dark Arts share one common feature: they free the practitioner from the immediate energy costs of his Arts but extract a far more severe price from him later on. Think of them as ways to convert some or all of the usual energy cost into a buildup of bad karma, alien taint, the Dark Side, Satanic influence, deformed p’o, psychic damage, or what have you. This Corruption – whatever its source – is resolved later on through such game mechanics as Will rolls, Calamity Checks, and conversion to disadvantages.

　Any of the above systems could be extended to other sorts of supernatural abilities. Provided that the capability in question costs energy (usually FP) to invoke, adaptation is straightforward. For example, demons might gift a man with a silver tongue – the better to spread their lies. This would work just like Black Magic, but instead of casting spells at reduced energy cost, the “dark preacher” would use Enthrallment skills (p. B191) without their usual FP costs, thereby gaining Corruption. Other potential Dark Arts of this kind include the Imbuement Skills of GURPS PowerUps 1 and the Energy Accumulating model of Path/Book magic in 『GURPS Thaumatology』.

　Some supernatural capabilities don’t have associated energy costs, though. Examples include many cinematic combat skills (e.g., Invisibility Art and Zen Archery), the Effect Shaping model of Path/Book magic, and almost anything from 『GURPS Powers』. For cases such as the first two of these, significant skill penalties are often involved, and the GM can allow the Dark Arts to diminish these in lieu of energy costs. Treat each -1 in penalties negated by the use of Dark Arts as a point of Corruption.
A similar principle applies to psionic abilities as described in 『GURPS Psionic Powers』: treat each +1 to the psionic skill roll as a point of Corruption. For supernatural gifts demarcated in levels – like most psi abilities – one-time access to higher levels is available at a Corruption cost equal to 1/5 of the character-point cost that the user would have to pay for the additional levels, rounded up. For instance, a dark psi with Telekinesis 2 [10] could strangle someone as if he had Telekinesis 10 [50] for a mere 8 points of Corruption.

　For the most part, none of these approaches work for the sorts of supernatural abilities that 『GURPS Powers』 describes. Those capabilities rarely cost energy to invoke and don’t always require rolls to use – and what rolls they do call for are seldom penalized. If you care to dig into the guts of the system, you can relate abilities to energy costs through the Temporary Enhancements and Trading Fatigue for Effect rules in Powers, and then model Corruption stemming from use of those abilities using whichever system you like from among those mentioned above. A simpler method is to use the Corrupting limitation (p. 22). Taking the limitation multiple times increases the amount of Corruption that each use of the ability causes.

　This is a relatively simple yet harsh Corruption system for magical horror campaigns that make corruption, temptation, and the dangers of power a major theme. With minor tweaking, it can represent the loss of sanity in a cosmic horror game. It presents sample answers to many questions that the GM should ask when tailoring a Corruption system to his campaign.

A Corrupt magus can claim “free” energy points to power any spell at the cost of adding an equal number of points to his Corruption total. The GM may impose a ceiling on these free points equal to six times the caster’s Magery level, sending him back to the blasphemous tomes or sulfurous pentacles for more learning. Spells cast using Corrupt energy risk the Black Critical Table from GURPS Magic.

If bought at character creation, every 10 points of Corruption is a disadvantage worth -1 character point.
Anyone – with or without Magery – can also gain Corruption by any of the following means:

Bad Places: Living in or traveling through a haunted house, a dark realm, or other Bad Place for a month adds 1d-2 Corruption. Some Bad Places add Corruption even faster; e.g., crossing the threshold of a lich’s tomb.
Engaging in any kind of magical rite (except possibly holy prayer or fasting) in a Bad Place adds 1d Corruption.

Blood Money: Profiting from the sale of an evil idol’s eye, spending cursed pirate gold, and similar transactions adds a point of Corruption per $1,000 involved. Some horrid wealth is worse yet: Spending one of the shekels Judas gained for betraying Jesus might add 5, 6, or more points of Corruption by itself, above its street value!

Corrupt Wounds: The bites, weapons, or talons of some creatures – demons, wraiths, vampires, and alien horrors especially – carry Corruption. Every point of injury received from such a monstrous opponent adds a point of Corruption.

Derangement: Every -1 in Derangement (p. 142) accrued adds a point of Corruption, as the sufferer beholds Evil’s grim glory.

Learning Hidden Lore: Every character point spent to gain Hidden Lore adds a point of Corruption. Some tomes – especially grimoires, or dark books used in Path/Book Magic – might carry Corruption even if they don’t teach Hidden Lore directly.

Using Cursed Artifacts: Using a cursed artifact for a mundane purpose adds 1d-2 Corruption. Using it for a ritual function (e.g., in a ceremony) or for an evil reason adds 1d Corruption. Using it to power or cause a supernatural effect adds Corruption equal to the energy points needed to cast the equivalent spell.

Vile Encounters: Eating human flesh or evil sentient fruit, sleeping with succubi, or otherwise mingling your life force with monstrosity costs 1d-2 Corruption per incident.

These consequences may be common knowledge, revealed in play by NPCs (“Go ye not to the graveyard on St. John’s Eve, lest ye be curst by Belial!”), or discovered only on a successful roll against Occultism (or Hidden Lore).

The GM keeps track of each PC’s Corruption total in secret, and is encouraged to lie like a demon when asked for a current total: “No, you feel fine. Better than fine! Your moral clarity is unimpaired.”