This trailer seems to suggest that injustice is cannon with the ending of Arkham City. Harley talks about how the joker is dead and that the joker in injustice aint the joker. So it its very possible that the joker in this game is actually clayface. It was a common theory after arkham city when clay face fell into the Lazarus pit, he went crazy and really believed he was the joker. I thought this had nothing to do with the arkham games, so that kinda freaked me out. This is like the persona 4 arena of the arkham games.