The PC version of Batman: Arkham Knight is a bit of a mess at the moment, but it’s also the only version with a mod that allows you to swap between any playable character in free roam with the push of a button.
Tired of playing as Batman? Press F2 and play as Harley Quinn, the crazed anti-hero on a quest to make up for bad DLC. Or F1 to clean up the street of Gotham City as the Red Hood, ultra-violent vigilante with surrogate daddy issues. There are ten additional characters in all, several of which I will not list as to avoid spoilers.
Warning—the video linked below as well as its YouTube description features character spoilers for Batman: Arkham Knight.
It’s all possible thanks to a mod created by Wastelander121 and MrJAG, now available for download via a link in the Batman Arkham Videos video description (via Polygon).
Between mods like this and Rocksteady’s ongoing patches and fixes, perhaps one the PC version will be remembered as the ultimate haha. Sorry.