Vengeful Harpy

Flying
Put {x} +0/+1 counters on Vengeful Harpy
where {x} is the amount of {b} mana used to
cast this card. If a spell or ability causes you
to discard this card, put it onto the
battlefield instead.
{1}: Sacrifice Vengeful Harpy. All players
discard cards from the top of their library
equal to the number of +0/+1 counters
on Vengeful Harpy.