Let's be honest, there's a ton of spooky mother fuckers in Arkham Knight. However, hands down, I think this particularly scary individual gives the others a run for their money, but to be perfectly honest I'm sure they wouldn't attest this opinion.
Warning!! There's a spoiler regarding the surprise mastermind behind one of the side missions in Arkham Knight, so read at your own risk.
Before [Batman: Arkham Knight](tag:2683936), I think it's fair to say Zsasz popped into many people's minds as being the most "unpleasant" antagonist in Rocksteady's Arkham series. The motive for his kills was freeing his victims from their mundane and idle lives. For each murder he'd cut a tally mark into his skin. Victor was determined to have Batman slayed and reserved a special spot on his body just for him.
What's tremulous about Zsasz was he could be anywhere at anytime, and know anything about anyone. As seen in Arkham Asylum when he recounted one of the doctor's at home evenings to exact detail while he was still a patient at the asylum. Up until Knight only Joker and Scarecrow associated with him, and he doesn't sit well with Catwoman.
Now, with that in mind, who could be worse than Victor Zsaz?
A demented scientist who vaguely looks like John Travolta and has pig like verbal tics that's who!! Professor Pyg aka Lazlo Valentin captured certain citizens who he wanted to make "perfect", and ended up mutilating their bodies into gender less, nearly indestructible automatons called Dollotrons. Rejects were hung up like deer in various spots in Gotham. Pyg had his sights on a bigger project...Batman.
Lazlo's obsession with "improving" people's appearances stemmed his parents' berating comments about his own looks as a child. If you listen to his audio files you'll learn he had a son through rape, and what happened to the mother. Dwight Shultz does a terrific job of portraying this disturbing miscreant. Honestly, I hope he gets nominated for his performance.
Believe it or not Pyg is a fairly recent Batman villain. His introduction was in Batman #666 which was published in 2007. He was also featured in Beware the Batman as an eco terrorist and was strangely British all of sudden (, but I didn't mind. his debonair voice was compensation enough). Yet, due to its child friendly tone he didn't appear in all of his morbid and derelict glory.