Zsasz
I must admit that I don’t know if Zsasz would be palatable to many audiences, but he would definitely fit the bill of an R-rated film and give Batman a new look at a different kind of baddie; one who’s a vigilante much like Bats and who takes pleasure in the simple things in life… like sadistically murdering his victims and notching each new scalp on to his skin.
The reason I include Zsasz at all is because of his role in Knightfall and later issues of the Detective Comics series. I’m particularly fond of the arc where Zsasz grows obsessed with hurting Alfred. He correctly identifies that there’s a thin moral line separating Batman from sheer anarchy, and he believes the Dark Knight enjoys inflicting harm on the guilty as much as Zsasz enjoys hurting the innocent. Can he get Bats to tip over the edge by hurting his precious Alfred?
Zsasz strikes at a charity event, stabbing Alfred and believing that his work is done. But Alfred survives and Bruce holds a press conference to lure the killer to the hospital where Alfred sleeps. True to form, Victor Zsasz can’t let his prey escape, and heads on over to finish his work. But Bruce is lying in wait, and the cat and mouse game has a happy result, though it’s not without its heart-in-mouth moments.
A similar gambit could be used in The Batman proper, don’t you think?