Giant Oyster

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.

Puedes elegir no enderezar la Ostra gigante durante tu paso de enderezar.
{T}: Mientras la Ostra gigante permanezca girada, la criatura girada objetivo no se endereza durante el paso de enderezar de su controlador y al principio de cada uno de tus pasos de robar, pon un contador -1/-1 sobre esa criatura. Cuando la Ostra gigante deje el juego o sea enderezada, remueve todos los contadores -1/-1 de esa criatura.