What would be really unique about Arkham Asylum Stage:
Have at least 12 known villains in there, most of which won't make the cut but are kewl to see: Mad Hater, Calendar Man, Killer Moth, The Riddler (talkin $h!t like usual lol), Two-Face, Hush, Deadshot, Mr. Freeze, etc. people that we really wont so much miss; yet also have 4 rather EPIC Bat-villain characters that are unlockable: Poison Ivy, Scarecrow, Killer Croc, and Bane. After you beat the game with a certain character on Very Hard or something similar the character will show up on the select screen and when you play on the stage again, it shows their cell busted open (Poison Ivy will have vines growing out her's, Killer Croc's inprint will be on the wall and shackles broken in his, etc.) Maybe even show a special lock on their cell that the others don't have, which we'll know their somehow unlockable (or even DLC with a Bat-Villain Extension Pack).
Phantom Zone Stage could house some pretty nice unlockable bad guys/gals too: Queen Bee, General Zod, Brainiac, and Doomsday and would actually relate to it's real use since each has actually been prisoned there.
Also Apokolips Stage could have 4 unlockable unique DC hero characters in Darkseid's prison cells: Zatanna, Plasticman, Red Tornado, Firestorm
Injustice League Swamp Headquarters could also contain cells for 4 more unlockable characters: Nightwing, Black Canary, Chameleon Boy, and Swamp Thing.
I think if the regular already playable kast only has Joker, Batman, Catwoman, Penguin, and Harley Quinn; and they use Captain Cold instead of Mr. Freeze then this would perfectly Balance the Bat-Kast (no need for Robin, Batgirl, Batwoman, etc.)
16 unlockable characters for beating the game with 16 other already playable characters would make a sweet 32 perfect kast of kharacters!!!
