In The Gamers Alliance, Kagetsu I begins working with the Grand Alliance against Arawn Losstarot when the Alliance saves Kagetsu's wife Marya from Arawn's stronghold. Likewise a group of clerics of MardŁk and Samachi work with the Alliance against the Northern Horde during the battle of Vanna despite their animosity which stems all the way from the Great War.
In Survival of the Fittest, Shameeca Mitchell and Heath Trennoby enlist the aid of Anti-Villain Bobby Jacks in order to mount a rescue from all around asshole Lenny Priestly. Admittedly Shameeca hadn't met Bobby before this point, but she was well aware that he was a killer.
In Chapter One of Off The Page And Into Life, Gail and Terrence have hated one another since childhood, in no small part thanks to their mutual interest in Henry. However, when MadameBlue begins spreading lies about them, they agree to work together to get rid of her. Gail even lampshades it, remarking that they're Not So Different, and probably would've taken over the world by now if they didn't hate each other so much.