The Dead Lands of Athas
Gray Zombies are spirits which have yet to be dissolved within the realm of the Gray. They have incredibly loose skin which hangs from their bony frames like an ill-fitting garment, and eyes that glow a bright green color. A gray fog billows from their mouth and any wounds they have taken.
Their connection with the Gray allows them to quickly regenerate wounds, which continue to weep a gray mist until they reconstitute. Their movement is never impeded by their loose flesh, and the beings can move with surprising mobility, attacking victims with their claws and teeth.
When gray zombies are destroyed, they disappear in a puff of gray smoke.