Giant Oyster is a special Creature — Oyster card from Time Spiral Timeshifted (TSB), collector number 22. Current market price: $0.29 (foil $6.44), TCGplayer market prices via Scryfall.
You may choose not to untap this creature during your untap step. {T}: For as long as this creature 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 this creature leaves the battlefield or becomes untapped, remove all -1/-1 counters from the creature.