Vampirism allows a character to transfer (bite) APs of Body from a target to his own Body. To attempt the action requires a check with AV/EVs equal to the APs of the Power and OV/RVs equal to the opponent's DEX/BODY; RAPS equal the number of APs transferred through the Vampirism bite. Any and all APs transferred through use of Vampirism will repair any body damage the character has taken and may never rise about the character's max Body attribute, but a character may use this as a form of attack to harm.
This type of power attack is always considered killing combat, as you are literally draining the life force out of another and should you drain enough to get the target to their negative Body Attribute, they will die and rise 24 hours later as a minor Vampire, with Vampirism Rank 1. If its a player character, the character is dead and now an NPC.
*Game Master's Note: I am aware there is a Vampirism power in later editions of DC Heroes and I probably could have ported that over, but I decided when I wrote it, I would change it up a bit making it a bite only attack, and the fact that if someone is killed by it, they rise as a minor vampire subservient to the now Master Vampire.