4. Killer Croc
Though there was a sly reference to Killer Croc in Christopher Nolan's The Dark Knight Rises, don't expect one of Batman's most famous foes to show up on screen anytime soon. Killer Croc aka Waylon Jones is a man born with a form of biological regression (aka atavism) that has bestowed him with a grotesque reptilian appearance. His villainy began when he murdered his aunt, who had mercilessly insulted his appearance, and in recent comic book arcs, Croc has become increasingly less human and increasingly more animalistic. Croc also has super-strength and speed, as well as regenerative capabilities and a thickened skin, all of which make him one of Batman's most feared enemies. His main issue is that, essentially, he's just not very smart, and is quickly outfoxed by Bruce Wayne most of the time. The main issue with bringing this one to the screen is that it's just so silly; short of going back to the Joel Schumacher route, this one's never going to happen.