Many people have probably discussed about Mr. Freeze, but I just wanted to bring up: What do you think if it was not just Mr. Freeze, but Mr. Freeze from Arkham City? That Mr. Freeze was AWESOME. The voice, suit design, everything about that Freeze was awesome. Think of the clash.
Batman, "This has to stop Victor." Freeze, "It stops, when your heart stops."
After Victor wins, he pulls out a snow globe with a figure inside (Hinting that it's his wife) "I draw nearer to you my Nora." Then it cuts to him standing before his frozen wife.
And who thinks they should bring in Black Canary, I mean hey it would be a good add on, think of what Green Arrow and her would say as they're about to clash:
Black Canary, "You're going to shoot a beautiful canary?" Green Arrow, "Don't take it personnel."
But most of all, Red Hood; think of the clashes that he could share with Batman, Batgirl, Night Wing, and The Joker?
Batman, "I don't want to hurt you Jason." Red Hood, "Then this'll be easy."
Batman, "Don't make me hurt you." Red Hood, "You left to me die, you can't do much more."
Night Wing, "You didn't deserve to be Robin." Red Hood, "You don't deserve to be alive."
Batgirl, "Jason this has to end." Red Hood, "It'll end, when your dead."
Joker, "I killed you!" Red Hood, "Now I'm just returning the favor/I had unfinished business/I just wanted to give you my parting gift."
Joker, "I killed you once, I can do it again!" Red Hood, "Just try."
Red Hood, "I'll make that grin disappear." Joker, "I'll make one appear, UNDER YOUR MASK!"