(Defenders of the Faith: A Guidebook to Clerics and Paladins variant, p. 79)
You gain an "Insanity score" equal to half your class level (add cleric levels to prestige class levels for this purpose). For spellcasting (determining bonus spells and DCs), add this score to your Wisdom score and use the result in place of Wisdom alone. For all other purposes, such as skill checks and saving throws, subtract this score from your Wisdom score and use the result in place of Wisdom alone. This means that your spells are very difficult to resist, but you are in general unaware of your surroundings and act imprudently—often erratically.
Once per day, you can see and act with the clarity of true madness. Use your Insanity score as a bonus on a single roll involving Wisdom, such as a Listen check or a Will saving throw. Choose to use this power before the roll is made.