List of (almost) all way to change form!

[Darg]

Warlock has the Spider-Shape lesser invocation, the Hellspawned Grace greater invocation, and the Dark Discorporation dark invocation.

Dragonfire Adept has the Humanoid Shape lesser draconic invocation.

Baleful polymorph and the Word of Changing invocation aren't on the list, but they are meant to be harmful so I don't know if they fit the theme.