Hey, It's That Voice!: To start, Batman, The Joker, Harley Quinn and Thomas Wayne are reprised by the actors who played them in Batman The Animated Series. Adrienne Barbeau, who was Catwoman in The Animated Series, is Dr. Whistler here. (Catwoman isn't in this game. She's not crazy.)
Steve Blum is Killer Croc, who has the voice of Vilgax. He's also a bunch of minor characters, including one in the opening sequence using a voice identical to Spike's. This would only be the first time he played a doctor in a video game.
Tom Kane is Commissioner Gordon. And Warden Sharp.
Or, for that matter, vice versa. Congratulations, gamers; you've heard Mr. Herriman call someone a bitch!
Dr. Penny Young is voiced by Penny. I wonder if that was intentional. (And Cree Summer's been in a Batman before: she was Max in Batman Beyond.)
Who knew that Ashley Williams used to be Batgirl and works as a doctor in between saving the galaxy? And according to IMDB, young Bruce Wayne as well. Also, like Cree Summer and Adrienne Barbeau, despite playing a different role, Kimberly Brooks already voiced somebody in some of the DCAU Batman stuff—Hello, Kathy Duquesne!
Poison Ivy has a second job, Fox-Hound sniper. And she also dabbles in Time Compression. In a minor example, Tasia Valenza also provided a voice for a DCAU character, though a very minor one (she was the voice of one of the servants sent to look after Max in the second part of "Curse of the Kobra" on Batman Beyond.)
An in-game example: Young Commissioner Gordon shares a voice with one of Joker's Mooks. It's disconcerting to hear the same voice that comforted Lil' Bruce threatening to stick a stun baton up Batman's ass.
If you are watching Avengers Earths Mightiest Heroes and wonder why The Absorbing Man sounds so familiar, Rick D. Wasserman is one of the main thug voices here, aka : *Get him on the ground and stomp on his face!*
Most of the dialogue from Harley Quinn's tapes is an almost word for word reproduction of Batman The Animated Series' Paul Dini's original origin story for Harley Quinn, Mad Love.
Enter the Visitor Center. Check out the Joker statue, turn away, and look back. It's posed differently now!
Maybe that's because it's not really a statue...
The same thing happens to Clayface in his cell; when you rescue the Warden, make a trip down to the cell and he'll look just like Sharp, and if you talk to him he'll claim you saved an imposter. Turn away, and you'll hear him shape-shift; a look back reveals he's turned into Commissioner Gordon.
A clue that Clayface isn't who he claims to be: if you look at him in detective mode, you can't see his skeleton.
Also, after you find Ra's al Ghul, be sure to stop by the morgue again later that night; his body will have disappeared.
The Arkham Care tie-in website lists its partners as Wayne Enterprises for the computer and security systems and Ace Chemical Processing for pharmaeceuticalsThe factory was the birthplace of the Joker, when he fell into a vat of acid that turned his hair green, and his skin chalk white.