New, highly stylized title is being developed as a prequel that revolves around Batman's first meeting with the Joker. It's based on the Silver Age of DC's comicbooks from the 1950s when the Caped Crusader teamed with other heroes like Superman and founded the Justice League of America.
Kevin Conroy and Mark Hamill voiced Batman and the Joker, respectively, in the previous games. Hamill has already said he won't be back to play the villain in the next game.
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This would be pretty cool. It would show that they are ready to change things unlike Sony Santa Monica.