Corrupt Spell

Prerequisite(s): Spellcaster level 1+, Any Evil Alignment
Benefit: This feat adds the evil descriptor to a spell. Furthermore, if the spell deals damage, half the damage is unholy damage. For example, a corrupted fireball cast by a 6th-level wizard deals 6d6 points of damage: 3d6 points of fire damage and 3d6 points of unholy damage. The corrupted spell uses up a spell slot one level higher than the spell's actual level. A character may take this feat multiple times, choosing a different spell each time.
Source: Book of Vile Darkness, Complete Divine