Camille

From Wikitrix

Camille is of an alien race called Sludgepuppies, a shapeshifting race in conflict with the Plumbers. She wants to make peace with Earth by marrying a Plumber whom she fell in love with. Strangely, her true alien form is human-like, as opposed to her familiy's monstrous appearance; however, she does initially appear like them, and simply takes on her humanoid appearance after meeting her future husband. Camille appears in "My Big Fat Alien Wedding".