5. Mr. Freeze
Doctor Victor Fries is one of Batman's most well known and popular villains, thanks largely to the Heart of Ice episode of Batman: The Animated Series (let's just forget about his appearance in Batman & Robin, shall we?). He's had several origin rewrites, but the most popular one sees Victor as a former cryogenics expert, who suffered an industrial accident while attempting to cure his terminally ill wife Nora. He's been given a new and interesting origin story in The New 52, which could act as a great launching-off point for an animated film. Victor's fascination with cryonics began as a child, when his mother fell into a frozen lake. The lake was cold enough that it kept her preserved long enough for help to arrive, which in turn prompted Victor's lifelong obsession with the cold. Nora is still a part of his villainous origin, though she's never his wife and is instead a cryogenically frozen woman on which he bases his doctoral thesis while working at Wayne Enterprises. Whichever origin they decide to adapt would be interesting enough to sustain a feature film, and give us a reason for caring about Victor enough to sympathise with his transformation into Dr. Freeze.