Dementor

Flying
{b}{b}{b}: Regenerate Dementor.
{b},{t}: Target creature gets -1/-1 counter. Put one
Dark counter on Dementor.
{b}{3},{t}: Exile target creture. Put one Dark
counter on Dementor.
{b}, exile all Dark counters: Dementor exile
creature with power is X or less when X is
number of Dark counters.