SRD:Enervation

You point your finger and utter the incantation, releasing a black ray of crackling negative energy that suppresses the life force of any living creature it strikes. You must make a ranged touch attack to hit. If the attack succeeds, the subject gains 1d4 negative levels.

If the subject has at least as many negative levels as HD, it dies. Each negative level gives a creature a –1 penalty on attack rolls, saving throws, skill checks, ability checks, and effective level (for determining the power, duration, DC, and other details of spells or special abilities).

Additionally, a spellcaster loses one spell or spell slot from his or her highest available level. Negative levels stack.

Assuming the subject survives, it regains lost levels after a number of hours equal to your caster level (maximum 15 hours). Usually, negative levels have a chance of permanently draining the victim’s levels, but the negative levels from enervation don’t last long enough to do so.

An undead creature struck by the ray gains 1d4x5 temporary hit points for 1 hour.