Vampiric Touch

Source vampiric touch

The spell's damage increases to 1d8 points of damage per 2 caster levels (maximum 10d8). Your melee touch attack to deliver the spell threatens a critical hit on a 19 or 20. This expanded threat range doesn't stack with other effects or abilities that increase the threat range. If the damage kills the target, you gain fast healing 5 for a number of rounds equal to the Hit Dice of the target.