Vengeance Ghast

Hexproof, unblockable.
When Vengeance Ghast enters the battlefield
choose target creature an opponent controls and
place a vengeance counter on it. So long as the
counter remains on the creature; it may be
sacrificed by its owner at any time.
At the beginning of your upkeep, if there is a
vengeance counter on an opponent's creature,
put a +1/+1 counter on Vengeance Ghast.
"You cannot escape it. Eventually you will beg
for death..." —Lord Dread