While we dont have to speculate about which final villain Superman will face, simply knowing its going to be Doomsday doesnt exactly provide all the answers. The prevailing thought is that that Lex Luthor somehow creates him. Zods corpse has been shown in his possession and its believed that Lex is attempting to investigate it to find a means of stopping Superman. From there, its possible that he activates some sort of failsafe in Zods DNA that transforms him into the monster. Conversely, its possible that Lex uses what hes learned and genetically engineers Doomsday as a living weapon. Comic readers, however will be familiar with Doomsday as an ancient Kryptonian monster that was exiled to the Phantom Zone to keep him away. Its unclear, however, if that will prove true in this film. Its certainly possible that he followed Zod out during Man Of Steel and just hadnt made it to Earth yet. So is he a mutated human, Zod's animated corpse, a test-tube monster or a rampaging alien? We know hes going to be a nearly unstoppable force that may go as far as killing Superman, we just dont know how hes going to get there.