As rumored before, it appears that the final act of Batman v Superman: Dawn of Justice will be a fight against Doomsday. However, something new appeared on the web today.
Batman will indeed fight Superman, but not at the end of the film – they will trade punches between the first and the second act of the film. And, much like Man of Steel, Batman v Superman: Dawn of Justice will also be light on action in the beginning.
However, the final fight promises to be a big one and will be switched between Metropolis and Gotham (most likely ending outside of the city). This isn’t all, since Doomsday will face not just Superman, but the DC Trinity itself: Batman, Superman and Wonder Woman.
Also, Doomsday is the character that finally unites the Justice League, at the very end of the movie, with several cameos from other superheroes also announced.
Source: Comic Book Movie