Giant Oyster

You may choose not to untap Giant Oyster during your untap step. {t}: For as long as
Giant Oyster remains tapped, target tapped creature doesn't untap during its controller's untap step, and at the beginning of each of
your draw steps, put a -1/-1 counter on that creature. When Giant Oyster leaves the battlefield or becomes untapped, remove all
-1/-1 counters from the creature.