Abattoir

Arnold Etchison is a regular old crazy person. A serial killer. The twist is that his victims are people he's related to, believing that he gains their strength when he kills them. I don't think he eats their brains or hearts or anything, but there's a limit to the gore you can have in all-ages Batman comics, so I bet they at least wanted him to. While acting as Batman, Jean-Paul Valley allowed Abattoir to fall to his death (which became part of the reason for Bruce Wayne to become Batman again). Etchison came back as a ghost in a later Batman storyline that's probably best forgotten.

Pros: No supernatural stuff (not counting the ghost part).

Cons: He's not all that interesting.

How I'd do it: You don't really have to change the character, except come up with some way for the audience to be frightened by him.

Casting Guesses: James Spader. I have no idea why, but I feel like he'd be a good crazy Abattoir.

Verdict: Nah. If you're going to have a regular crazy murderer, Zsasz is the best choice.