The Skeleton King

Menace, deathtouch
Whenever a creature an opponent controls dies,
create a 1/1 black Skeleton creature token.
{t}, Sacrifice X Skeleton creatures: You may cast
target instant or sorcery with mana value X from
your graveyard this turn without paying its mana
cost. If a card cast this way would be put into
your graveyard, exile it instead.