Continuity mistake: In the beginning, Bruce Wayne drives his car towards all the chaos, but the crowd is too thick for him and his car to get through, but with movie magic suddenly Bruce and his car are at the front of the crowd. (00:07:00)
Continuity mistake: When Batman goes to save Martha, he pulls the wooden box with his gun and throws it at one bad guy. The guy's head hits the wall, leaving blood. Later on, you still can see the dead guy but there is no blood on the wall any more. The blood appears again when Batman is about to finish off the last person who was stabbed and pinned against the wall. (02:17:30 - 02:18:35)
Continuity mistake: Superman gets his hair messed up during his fight with Batman, but while he is fighting Doomsday his hair is perfectly combed again.
Continuity mistake: After the mercenaries kill everyone in the desert, there are two guys looking at them using two monitors. The pencil below them changes from white to blue.
Continuity mistake: When Perry asks Clark to do the sports note he has the paperwork in his left hand but in the next shot he is holding it in his right.
Continuity mistake: After Batman shots the tracking device onto the truck, later in the warehouse the device is next to a number 5 that was not there before.
Chosen answer: It is Flash. He is wearing armour because of whatever has transpired in the future. He often wears an armoured suit in dire circumstances in the comics.
Also, if you look at the bottom of the image frame you can just make out the Flash icon on his chest piece.