Arkham Origins: Joker, Deathstroke, Bane, Mad Hatter, Deadshot, Copperhead, Bronze Tiger, Firefly, Enigma (the Riddler), Electrocutioner, Shiva, Harley Quinzel (later Harley Quinn), Mr. Freeze, Roman Sionis (Black Mask) and Killer Croc
Arkham Asylum: Joker, Harley Quinn, Poison Ivy, Killer Croc, Scarecrow, Bane, the Riddler, and Zsasz
Arkham City: Joker, Harley Quinn, Clayface Joker, Professor Hugo Strange, Ra’s al Ghul, Bane, the Penguin, Two-Face, Zsasz, Poison Ivy, Mr. Freeze, the Riddler, Solomon Grundy, Deadshot, Clayface, Mad Hatter, and Hush
Harley Quinn’s Revenge: Harley Quinn
Arkham Knight: Scarecrow, Harley Quinn, Poison Ivy, the Penguin, Two-Face, Man Bat, Arkham Knight (Jason Todd/Robin), Mr. Freeze, Firefly, Professor Pyg, and Killer Croc
Gotham Knights: Court of Owls
Suicide Squad: Kill the Justice League: Brainiac, Superman, Batman, Wonder Woman, any Green Lantern, Aquaman, Cyborg, the Flash, and the rest of the Justice League.