As far as I know - Aizen helps Ichigo and others to fight Yhwach (another PE) since Aizen "destroys everyone who tries to control him" and sees Yhwach as bigger threat to his own freedom......... But, to be honest, I'm 99% sure that if Bleach story will continue - Aizen will kinda redeem himself.

Frieza helps Goku in the Tournament of Power. Joker helps Batman take down TBWL.

Darth Krayt and Luke Skywalker teamed up to fight Abeloth.

The Phantom actively helps Wright and friends solve cases multiple times solely to preserve his facade.

Alpha helps the Men in Black stop Vangus because he wanted to rule over the planet and Vangus was planning to destroy it.

Slade helping the Titans defeat Trigon