Some humans willingly offered up their blood, hoping it would grant the vampire families the strength to stave off the Eldrazi.

Bloodthrone Vampire

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

The List

Duel Decks: Zendikar vs. Eldrazi

Modern Masters 2015

"What I need is your blood. What I don't need is your permission."

Magic 2013

URL/Convention Promos

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.

You can sacrifice Bloodthrone Vampire to activate its own ability, but it won’t be on the battlefield to get the bonus.