You can transform one of your spells into an evil version of itself.
Prerequisite: Any evil alignment.
Benefit: This feat adds the evil descriptor to a spell. Furthermore, if the spell deals damage, half of the damage (rounded down) results directly from divine power and is therefore not subject to be reduced by resistance or immunity to energy-based attacks.
A corrupted spell uses up a spell slot one level higher than the spell’s actual level.
Source: Complete Divine, page 79.