If you need realistic Villains then it does seem like mr. Freeze would be out. Yeah you could make him a guy who keeps his victims in a freezer, and you can have clayface as a master of disguise, but at that point what's the point?
Guys who are just nuts or psychos like Scarecrow, Professor pyg, black mask, Firefly, two face, zsasz, calendar man, mad hatter, even king tut could work more easily. You could have a guy with a skin condition and make him killer Croc. Bane is possible.