Batman

The last trailer revealed a Batman we have never seen on-screen. This version of the Dark Knight is far-far more brutal than the previous ones. And even if we saw his symbol branded onto a villain's chest, we didn't expect for him to break so many bones when fighting (the guy whose face was punched into the floor "“ did he survive that?!?).

Also, the final trailer specifies that he is old. In fact, he is too old to die young at this moment. And this also makes him a bit more paranoid, which in a way justifies his feelings towards Superman and, basically, everybody who possesses superhuman abilities. And this makes us wonder if he will cross the line and ally himself with hidden villains.

We are more than certain that Bruce Wayne (the world's greatest detective) has some idea about Lex Luthor's agenda. Which would make such an alliance even more surprising. But, at this moment, we are open to any possibilities. At some point in the trailer, when Lex Luthor creates Doomsday, he says “If man won’t kill god, the devil will do it!" Is this a nod toward this alliance? To be noted, Superman is right behind him when he says that.

What can two of the greatest minds of the DCEU do to defeat Superman? Well, they can certainly come up with the schematics of a Mech suit that matches the power of the Man of Steel. They can work together in order to discover that kryptonite is the weakness of the alien. They can actually do a lot of things.

But something will happen, and Batman won't go the extra mile to kill Superman. And, at this point, Luthor's initial plans are foiled, so he creates Doomsday, which ultimately works against him (since Wonder Woman also joins the fight). This is just speculation, though, so it should be taken with a grain of salt (not too much, though).

Also, the final Batman v Superman trailer revealed one more thing: Bruce Wayne/Batman has no idea who Diana Prince is. Which leads us to suspect that the latter joins the fight after a long break (at this point, we are almost certain that she operates more than covertly during WWI, in her solo flick).