5. Killer Croc
In the Batman comics, Killer Croc was born as a human, but had a skin condition reminiscent of epidermolytic hyperkeratosis. In addition to the presence of a metagene, this endowed him with enhanced versions of the abilities associated with the reptilian ancestors of the human race. He has near impenetrable skin, is quick, strong and agile and has razor-sharp claws and teeth. He would represent a monstrous physical threat to Batman - the kind of which has yet to be seen in any of the live action Batman movie adaptations. Even the two versions of Bane that we've seen on screen don't come close to him physically. With modern CGI, he could look fantastic too and he would be one hell of a baptism of fire for a new Batman to have to deal with. The only problem is that the character himself is actually a bit lame but, coupled with another villain (one who is more associated with scheming and plotting), his physical threat and awesome appearance could make for fantastic big-screen viewing.