I think they will use the Penguin, Black Mask, KGBeast,and the Riddler. I think the sequel will be a good time to introduce the character Hush, if he is to be seen on the big screen in any Batman film. They could have him appear briefly in the shadows and have him be a major player in the 3rd movie. Hush could just appear in the shadows watching over things. He could be the secret ring leader of everthing that is going on in the sequel. The Joker, The Penguin, and the other villians could secretly be working for him or they could be working for him and just don't know it. Hush could introduce himself to Batman in the 3rd movie revealing he told the Joker to throw acid into Harvey Dent's face so he could go insane and become a dangerous criminal and he was using all these criminals to start a huge gang war. The 3rd movie I think should be based on the War Games books.