Arkham Origins multiplayer centers on a gang war between the Joker and Bane.
The main multiplayer component, Invisible Predator Online, places three Joker gang members against three Bane gang members, with Batman and Robin entering the same match as a third force. The gang teams fight to eliminate the opposing gang’s reinforcements, while Batman and Robin pursue intimidation points by taking down gang members.
The mode gives both villain factions their own weapons and explosives, while Batman and Robin use gadgets and abilities adapted from the single-player campaign. A gang member can also become a boss character—Joker or Bane—with stronger abilities, reinforcing the rivalry at the heart of the mode.
Black Mask is a major figure in the single-player story, but he is not the opposing gang leader in Arkham Origins multiplayer. Two-Face and Penguin likewise do not form the game’s central multiplayer faction. That distinction between the campaign’s villain roster and the multiplayer teams makes Bane the canonical answer.