For any of you who have played Conan Exiles, this is the rule for corruption that I use. It has some attractive elements that let Stealth and Sorcerer players take on some additional risk to increase their effectiveness. As well as a way for a GM to rein in the effect if things get out of hand.
Corruption is an element where the character is infected with the outer dark. Corruption causes the character to have one less wound and trauma than they normally would be allowed, though they do not take any other penalty. (A character that would die at five wounds now dies at four wounds.) If a character has five corruption, then they fall under the control of one of the elder gods. If this happens to a player character, then they become a permanent non-player character under the GM’s control. A character can not have more corruption than they have wounds, and a character at max corruption will die if they take any loss to vigor or resolve.
Anytime powerful elements of the outer dark are encountered in the world, the GM has the option of spending 1 or more doom to force the characters within medium range of the source of corruption to roll either a resistance or discipline check, selected by the player, with the difficulty equal to the half the doom spent, rounded down. This effect should only occur in areas of the world tainted by the outer dark or when treating with an elder god. Players should be warned ahead of time that they are crossing into a corrupting area by the unnatural feeling sinking into the character’s bones. While a character has at least one point of corruption, they are treated as though they have the unnatural trait for the purpose of traits such as witch hunter or demon slayer.
If a character wishes to, they may voluntarily take one corruption per scene without a roll if they have some sort of interaction with the outer dark, left up to the GM’s discretion. While a character has at least one point of corruption, all social tests are raised in difficulty by the number of corruptions that character has, while intimidation and threaten actions are reduced by the same amount. A character gains bonus momentum equal to each point of corruption for all tests involving stealth or sorcery. When a character with corruption attacks a creature with unnatural armor or courage, such as incorporeal, the corruption grants one bonus momentum per point of corruption that can only be spent on the piercing momentum spend.
Removing Corruption: When the characters are able to rest for a scene they may attempt a resistance or discipline test with a difficulty equal to the number of corruption points they have. Success indicates they lose one point of corruption, with bonus momentum used to prevent fatigue or despair on a one for one basis. Each point of corruption lost results in the character gaining one fatigue and one despair. During the carousing phase of an adventure, all points of corruption are lost with the fatigue and despair penalty negated. Characters cannot choose to keep their corruption through a carousing phase.
Alternatively, the GM may remove corruption from the character without the fatigue or despair penalty if the character is on sacred ground, such as a temple to Mitra, or in the presence of something the character would consider holy or serene.