Living foes damaged by your spell also gain a negative level.
Benefit: You can alter a spell that deals damage to foes so that any living creature that is dealt damage also gains a negative level. If the subject has at least as many negative levels as Hit Dice, it dies. Assuming the subject survives, the negative level disappears (without requiring a Fortitude save) after a number of hours equal to your caster level (maximum 15).
A fell draining spell uses up a spell slot two levels higher than the spell’s actual level.
Source: Libris Mortis, page 27.