He can be creepy without prosthetics. Now, with the eyes they could give him creepy eyebags, and maybe some contouring to accentuate certain parts of the face like the chin, mouth, etc.
I totally get the appeal of a freakish Joker with prosthetics, believe me. An ASHOSE-esque Joker would be fantastic, but I'd like for them to make it look natural (as natural as that version CAN look, anyways). I dunno, I've just always been intrigued by the more human-looking versions of the character, mainly in movies and in the recent Joker: Killer Smile and Batman: The Smile Killer miniseries.