Bloodthrone Vampire
Creature — Vampire
Sacrifice a creature: This creature gets +2/+2 until end of turn.
Some humans willingly offered up their blood, hoping it would grant the vampire families the strength to stave off the Eldrazi.
Steve Argyle
Rulings
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 the creature you wish to sacrifice is dealt lethal damage, it'll be destroyed before you get a chance to sacrifice it.
(wotc • 2010-06-15)
You can sacrifice Bloodthrone Vampire to activate its own ability, but it won't be on the battlefield to get the bonus.
(wotc • 2010-06-15)
Rulings
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 the creature you wish to sacrifice is dealt lethal damage, it'll be destroyed before you get a chance to sacrifice it.
(wotc • 2010-06-15)
You can sacrifice Bloodthrone Vampire to activate its own ability, but it won't be on the battlefield to get the bonus.
(wotc • 2010-06-15)