Arykargor, Shadow Blight

Swampwalk (This creature can't be blocked
as long as defending player controls a swamp)
{x}, {t}: Exile target card with converted mana
cost X or less from a graveyard. If X is 4 or
more, you get an experience counter.
At the beginning of each opponent's upkeep,
that player loses X life, where X is equal to the
amount of experience counters you have.