If there's one thing the Batman: Arkham series has made sure of, it's that as many characters as possible from the Dark Knight's comics are placed within the games themselves. Between boss fights, side quests and even little bits of lore, even the more obscure hero, villain or supporting character has a decent chance to find themselves in the triple-A title.
However, this isn't to say that every character has snuck their way into the game. With Batman having such an expansive list of allies and enemies behind him, the potential to add yet more new faces is basically boundless.
On a similar level, there are characters who have previously appeared in a minor role, who maybe deserve a more major role in a new entry. With each Batman game being bigger than the last, there's likely room for other characters to have a more prominent feature without cutting the Caped Crusader's screen time too much.
From alternate universes to characters left in the eighties, the capacity for yet more unusual characters to star in the next Batman game - said to be a sequel to Arkham Origins, featuring the Court of Owls as villains - is equal parts exciting and overwhelming.