Batman: Arkham Knight introduced a new system where in certain sections of the game Batman could team up with his various allies for some dual-vigilante action. These secondary characters are only playable in certain areas, but a mod has unlocked them and allows you to play as any of them whenever you like.
The Batman: Arkham Knight Playable Characters mod makes Red Hood, Harley Quinn, Nightwing, Robin, Azrael, Bruce Wayne, Catwoman, Commissioner Gordon, the Joker, and GCPD Officer Owens available to play as instead of Batman. You can see them all in action in the video above. The mod only works for free-roaming Gotham City.
You can download the mod here, and instructions for installing are in the YouTube video description. Remember this isn’t a Steam Workshop mod, so backup your files, and do so at your own risk.
Of course, you’ll only want to install the mod provided you’re one of very few people who actually have Batman: Arkham Knight running acceptably on your system. Thanks to a disastrous launch filled with bugs and glitches, Arkham Knight has been withdrawn from sale, and you can get a refund on the game from Steam should you wish.