Vampire Aristocrat

Oracle Text

Sacrifice a creature: Vampire Aristocrat gets +2/+2 until end of turn.

Card Rulings

10/1/2009 You can sacrifice Vampire Aristocrat to activate its own ability, but it won’t be around to get the bonus.
10/1/2009 If you sacrifice an attacking or blocking creature during the declare blockers step, it won’t deal combat damage. If you wait until the combat damage step, but that creature has been dealt lethal damage, it’ll be destroyed before you get a chance to sacrifice it.