Skeletor
Mumm-Ra was granted incredible magical powers by the Ancient Spirits of Evil in exchange for an eternity of perpetual servitude. His weaknesses include his own reflection, and his limited stamina. He often needs to return to his Pyramid to regenerate.
Skeletor was granted incredible magical powers by Hordak in exchange for releasing the Horde from the dimension of Despondos. After receiving his powers, Skeletor sealed them in Despondos forever. He has no known weakness.