Help wanted to think on house rule - Magic Corrupts

[xzyx]

So I'm going to DM this campaign to some friends next week, on which we'll make a try with the pathfinder system. It's an old campaign I had made long ago and that I like a lot. The reason I'm post here then? I wanted to make a house rule, but I'm not sure on how.

In this setting I made, arcane magic corrupts people. When spellcasters use arcane magic, they force their will to change the enviroment, and that creates entropy, and such entropy is then forced into the spellcaster as a backlash of his magic - making him crazy over time and essentially transforming most magicians in power-hungry bastards over the years. The first time I DM'd it the group had no arcane spellcasters so I did not have to worry about the effects of corruption over the players and it was mostly present on the setting. But now, I have at least two full caster arcanists in the group (a summoner and a sorcerer) and I would like to have some kind of system that reflects this element on the setting, but I wanted it to be well done and as simple as possible. After thinking a lot, I couldn't come up with a good way to implement this, so I come to you, minmaxers. Do you know of any way to represent magic corruption on the game?

[Garryl]

Here's an idea off the top of my head. It's not fully thought through or anything.

(click to show/hide)

Using arcane magic corrupts the spellcaster. Divine magic, being filtered through and controlled by the gods, does not carry this risk.

You accumulate arcane corruption. Initially, your arcane corruption begins at 0. Casting arcane spells  and using arcane spell completion items (including in the creation of magic items) causes arcane corruption. Whenever you cast an arcane spell, you gain arcane corruption equal to the spell's level. Using an arcane spell completion item causes half spell's level in arcane corruption, rounded up. More powerful spellcasters, having greater control of their powers, can mitigate this somewhat. For every 3 levels of the highest level spell you can cast, the amount of arcane corruption you gain from employing an arcane spell is reduced by 1 (minimum 0).

Arcane corruption can never drop below 0. Any time it would be reduced below 0, it is instead reduced to 0. There are two ways to remove arcane corruption. The first is time. For every 24 hours spent without casting any arcane spells or using any arcane spell completion items (even ones that do not cause any corruption), you lose 1 point of arcane corruption. The other method is divine magic. A restoration spell removes 1 point of arcane corruption from a subject who has not cast any arcane spells or used any arcane spell completion items within the past 24 hours. A greater restoration spell removes 3 points of arcane corruption from a subject who has not cast any arcane spells or used any arcane spell completion items within the past 24 hours, or 1 point from one who has. Only when these spells are cast as divine spells do they remove arcane corruption; spells cast as or emulated by arcane spells cannot remove arcane corruption.

Small amounts of arcane corruption are tolerable. Your arcane corruption threshold is equal to your character level + your Wisdom modifier + your Charisma modifier (minimum 1). As long as you have less arcane corruption than that, you suffer no penalties at all. For each multiple of your threshold, you suffer a cumulative -2 penalty on Concentration checks, to a maximum penalty of -10. At greater multiples of your threshold, you suffer additional penalties, as indicated below. Effects listed in the "Special" column are cumulative (you suffer the effects of all lower arcane corruption threshold multiples as well as your current multiple).

Threshold Multiple	Concentration Penalty	Special
0	-0	--
1	-2	Hostility
2	-4	Consumption
3	-6	Partial Insanity
4	-8	Compulsion
5	-10	Insanity

Hostility: Once your arcane corruption reaches or exceeds your threshold, animals can feel your corruption. Creatures of animal intelligence (1 or 2) and mindless vermin naturally shy away from you. Their initial attitudes when meeting you are always Unfriendly or worse. Even those that know you and are used to your presence will never have an attitude better than Indifferent. Even intelligent creatures can sense your corruption, and while they may not be able to tell what exactly repulses them from you, they are aware of it on at least an unconscious level. Creatures with intelligence 3 or greater whose initial attitudes towards you would be Indifferent are instead Unfriendly, those with initial attitudes of Friendly are instead Indifferent, and those with initial attitudes of Helpful are instead only Friendly.

Consumption: Once your arcane corruption reaches or exceeds twice your threshold, you become physiologically addicted to arcane magic. Each day that you do not cast any arcane spells or use any arcane spell completion items, you must make a Fortitude save (DC 15 + 1 per day since employing arcane magic) or suffer 1d6 points of nonlethal damage. This nonlethal damage cannot be healed until you use arcane magic or until your arcane corruption drops to less than your threshold.

Partial Insanity: Once your arcane corruption reaches or exceeds three times your threshold, a mild form of insanity begins to take hold of your mind. This frequently manifests itself as megalomania, but other conditions are possible. At this degree of corruption, the insanity is manageable, and is never debilitating. However, it cannot be treated until your arcane corruption is reduced below your threshold.

Compulsion: Once your arcane corruption reaches or exceeds four times your threshold, the use of arcane magic becomes an addictive craving. Each day that you do not cast any arcane spells or use any arcane spell completion items, you must make a Will save (DC 15 + 2 per day since employing arcane magic) or be compelled to cast an arcane spell or use an arcane spell completion item. If you are unable to do so, you suffer 2 points of Wisdom damage. This Wisdom damage cannot be healed until you use arcane magic or until your arcane corruption drops to less than your threshold.

Insanity: Once a character's arcane corruption reaches or exceeds five times her threshold, it controls her. She becomes fully insane (depending on how this insanity manifests itself, this may not be entirely debilitating to the character). The character becomes an NPC under the control of the DM. This insanity can never be fully cured, even if the character's arcane corruption is completely purged.



For example, Archmage Solberg is a 14th-level Wizard, with an Intelligence of 20, a Wisdom of 12, and a Charisma of 14. His arcane corruption threshold is 17 (14 + 1 + 2). Due to his mastery of the arcane arts (being able to cast 7th-level spells), Solberg can cast 0th-, 1st-, and 2nd-level spells without risk of corruption. For higher levels spells, he gains arcane corruption equal to the spell's level minus 2. As such, he can safely demonstrate the magic that he teaches his apprentices in his tower, although his teachings are still filled with warnings about the danger involved for less experienced mages.

When an orcish raiding party threatens a nearby village, the archmage is called forth to defend it. Unleashing his awesome power, Solberg drives the orcs away. In the process he casts 3 3rd-level spells, 2 4th-level spells, 2 6th-level spells, a 7th-level spell, and an assortment of his 2nd-level and lower spells. In the process he gains 20 points of arcane corruption (3x1 + 2x2 + 2x4 + 1x5). Being the cautious and experienced archmage that he is, Solberg made sure to purge himself of arcane corruption thoroughly after his previous adventures, so these 20 points are all he has. Since he has now exceeded his arcane corruption threshold, his thoughts feel mildly fuzzy (a -2 penalty on Concentration checks). As Solberg now radiates a subtle aura of corruption, he does not receive the hero's welcome he expected. The town mayor is thankful for Solberg's efforts, but politely cuts their meeting short (Friendly instead of Helpful). Most of the townfolk give the mage a brief nod, but little more (Indifferent instead of Friendly). The village priest, who has always distrusted arcane magic, goes as far as picking an argument with the mage when they pass in the street (Unfriendly instead of Indifferent). Even Solberg's apprentices seem distant in their lessons later in the day. However, after a four days' rest, during which Solberg avoids any spellcasting in his lessons, the archmage's corruption drops to 16, less than his threshold of 17, and good cheer returns to the tower.

[veekie]

^^
Looks workable, but I'd personally eliminate the potential to remove the corruption via spells, since it allows for the mechanic to be bypassed at a small wealth tax. I'd also throw in a bribe factor, encourage them to flirt with the limits.

An alternative idea:
You accrue corruption through the casting of spells, the amount of corruption is equal to twice the spell level. Corruption naturally fades at a rate of half your caster level each day(total, meaning if you have corruption in all three tracks you'd have to split it up), and by your full caster level if you do nothing but purify yourself that day(naturally without casting any spells). When an increase in corruption crosses a threshold, you gain a symptom of the corruption. The symptom persists even if corruption decreases below the threshold, but cannot be removed unless your corruption is below the threshold that caused it and you have not increased that form of corruption that day. You can have a maximum of one symptom per category, plus one for each higher severity you have in that category(E.g. If you have a Critical Symptom, you can have 2 Serious symptoms, 3 Moderate symptoms and 4 Light symptoms).

Corruption Thresholds(threshold benefits apply only as long as you stay at least at that level of corruption):
Light(Corruption > CL) - Minor, cosmetic signs that can be concealed with care. Quirky, but not really a problem unless you're trying to pass for normal. Your effective caster level for this type of magic increases by 1, but it doesn't improve your corruption capacity.
Moderate(Corruption > CL x2) - Noticable signs which make it clear you're heading towards crazytown, which may also cause some loss of control. You gain another caster level for spells associated with the corruption., which likewise does not improve corruption capacity.
Serious(Corruption > CL x3) - Symptoms at this point come with minor perks, such as sensory augmentation, natural weapons, or even the ability to inflict a lesser form of your own problems onto others. You gain a bonus spell slot at your highest spell level, which can only be used to cast or prepare spells of this type.
Critical(Corruption > CL x4) - Major changes start to kick in, and you might not be considered human(oid) in some areas anymore, though you do gain significant perks from the mutation, you also start losing control of yourself. The bonus spell slot from the Serious threshold expands, you get one at every spell level you have access to.
Final(Corruption > CL x5) - Transformation. Mental corruption overwrites you with a parasite personality entirely, Physical corruption turns you into an undead, aberration or some other monstrous creature. Environmental corruption turns you into a living spawnpoint for another dimension, and replace you with an outsider of the appropriate type to boot. As far as the game is concerned you're dead.

Three types of corruption are available:
-Mental Corruption - The use of Divination, Enchantment and Universal spells fosters Mental Corruption. The hallmarks of this corruption are mental tics, phobias, hallucination and ultimately, insanity. Mental Corruption is offset by your Wisdom modifier, each time you gain corruption, you reduce it by your Wis mod, or increase it, if your wisdom modifier is negative.
-Physical Corruption - The use of Abjuration, Necromancy and Transmuation fosters Physical Corruption. The hallmarks of this corruption are disfiguration, mutation and ultimately transformation. Physical Corruption is offset by your Constitution modifier, each time you gain corruption, you reduce it by your Con mod, or increase it, if your constitution modifier is negative.
-Environmental Corruption - The use of Conjuration, Evocation and Illusion fosters Environmental Corruption. The hallmarks of this corruption is the twisting of the environment around the caster, ultimately resulting in a reality breach. Environmental Corruption is modified by the location, with a minimum of -5. Particularly pure locations reduce the corruption by -5, however, each spell that causes Environmental Corruption cast in an area increases the modifier by their spell level after the corruption check, and this fades at the rate of 1 a day.

If there's any interest in this I could try cooking up some sample symptoms for the corruption types.