6. The Riddler
It was a major disappointment to many Batman fans that Christopher Nolan never took on The Riddler, and after much speculation that he would finally do the character justice in The Dark Knight Rises, he instead opted for the far riskier prospect of Bane. The Riddler character was played by Jim Carrey in Batman Forever, and though the movie itself is wildly divisive, Carrey did deliver an energetic and entertaining performance, even if something more grounded and subdued would be needed for any future take on the character.
The Cameo: Given that the movie is already going to be dealing with Lex Luthor, Snyder would be smart to plant the seed but leave it to grow. As Warner Bros. should do well to take as many pages out of Marvel Studios' book as possible, it would make sense to use a post-credit scene to tease the next movie, and some sort of introduction to The Riddler would be very smart. It doesn't need to be overt or show the man in his get-up, but perhaps it would be a shadowy allusion to Edward Nygma, or Bruce receiving a riddle of some kind?