Wyverns are giant winged reptiles in the service of Skeletor.  Making their home at the Vale of Caldor, a large lava lake surrounded by Ice Mountains, they make great guardians for captives, as they are kept at an island in the middle, so that if anyone tries to rescue them, a Wyvern could quickly fly in before the rescuer could reach the middle.

Wyverns can see just as well in the dark as in the light, howvever, they can be blinded by steam.