Both are final bosses that usurp the power of a deity and plague the world that the deity ruled over. Both are fought multiple times (Nightmare is every dungeons' boss), one of which is an embodiment of a previous villain (BellumBeck is a phantom and Nightmare's Ganon form). Both leech of of the power of their respective deity (The Nightmares prolonging the wind fish's slumber and Bellum even being called "The Life Leech"). --Hydropanda (talk) 16:51, December 27, 2010 (UTC)