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.
Near Mint - $0.30
Near Mint Non-English - $0.30
Lightly Played - $0.30
Lightly Played Non-English - $0.30
Played - $0.20
Played Non-English - $0.20
Heavily Played - $0.20
Heavily Played Non-English - $0.20
Damaged - $0.20
Damaged Non-English - $0.20