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People think that the guy who tried ot blackmail Batman, whose name is Mister Reese (Mysteries) might end up being the Riddler, whose name was previously E. Nigma (Engima).

the rumor is that the riddler might be in the next batman movie, he was not in the dark knight.

Im not so sure but I do recall a Catwoman reference when Fox refers to the Bat suit being "cat proof" when Bruce asks if it is "dog proof" or something like that. He mentions cats....

there is a possibility of a black mask reference(aboard the Joker's ferry) and a catwoman in-joke(the new batsuit being cat-proof)

Other bat references include the commissioner being named after uber talented writer Jeph Loeb

there wasn't one.....

I mean two face and joker were the only villians

there was no foreshadowing of another future villian