Ji-Woon Hak, the Trickster

Flash
Showstopper — Whenever a spell is cast, you may
put a -1/-1 counter on target creature if you control
that spell. If that spell is controlled by another
player, that player may remove a counter from
target creature he or she controls.
{u}{b}{r}, {t}: Destroy each creature with three or
more -1/-1 counters on it.