There are two parts to this one and it all begins with Geeky Tyrant, who apparently spoke to an on-set extra who told them "the ending of the film has already been filmed. One of the scenes shot featured Batman breaking into Lexcorp to steal kryptonite, and apparently Lexcorp had somehow gotten ahold of General Zod's body."
So just in that first little bit we've got Kryptonite, Lex Luthor, General Zod, and Batman possibly getting his hands on the one thing that can stop Superman. Badass Digest then confirmed much of it, adding that Luthor has been gathering pieces of the World Engine, and plans to use Zod's corpse as the central part of his plan. What's he going to do with it? Create something, or someone, who can finally defeat Superman of course. They tease that enemy with this:
Looks like the outline of Doomsday, doesn't it? This isn't the first time Doomsday has been rumored to be making an appearance and it probably won't be the last. What do you think? Batman v Superman: Dawn of Justice opens March 25th 2016.
