Unleash the Plague

Put a Plague counter on target creature. (Creatures
with Plague counters on them have at the beginning
of your upkeep if this creature has no -1/-1 counters
on it put a -1/-1 counter on it. Then put a Plague
counter on another target creature you control that
doesnt have Plague counter on it. If at anytime
all creatures a player controls have Plague counters
on them that player must sacrifice all creatures
they control)