3. Flamingo
Who Is He? Think Prince meets Anton Chigurh and you've got a good idea as to what Flamingo is all about. Created by the incomparable Grant Morrison, Flamingo is a psychotic hitman who was lobotomized so that he wouldn't feel anything while butchering his prey. He's a sociopath with the style of an 80's pop star and kills with the ferocity of a starving mountain lion. Only appearing in a few Batman issues, and always as a mindless killing machine Flamingo has yet to reach his full potential as a member of Batman's rogue's gallery. This is unfortunate of course because there's a lot that could be said about a guy who's nickname is "The Eater of Faces." On second thought, probably the less said about that the better.
How Should He Return? Flamingo doesn't require any character tweaks, because his weirdness is part of what makes him so interesting. Just set up a situation where someone in power wants Batman dead (like aforementioned Monarch) so he hires Flamingo to do the job. Now Batman has to run from a guy that wants to have his dimples for dinner, all the while trying to crack the case as to who wants to see his face on Flamingo's dinner plate. Since The Dark Knight spends the majority of his time tracking down criminals, it would be an interesting situation to see Batman on the other end of the chase for once.