I think they said they wanted to shine a light on some villains not yet displayed in movies, so I think we're looking at something Burton didn't use at all. I'm guessing they don't want their characters tied to something comparatively lame, like Mr. Freeze and such (I think they also wrote off Poison Ivy as well). Joker was obviously a safe bet, because you can't really avoid him in a Batman franchise + who doesn't want to be remotely connected to something portrayed by dear ol' JackTom Goldman said:snip