Carly

Carly is Finn's best friend and Billy's boyfriend from Finn 10: Fusion. She was mutated by the Moutater, but a nuclear reactor was leaking and spilled on her at the same time. She can turn into a handful of Finn's aliens, and a bunch of other things, too. She is always discovering forms. Each form has a power that the regular alien doesn't have.

Petrosapien Form
Carly always keeps her left hand a point. She can also turn intangible. When she is angry, she turns red and melts into water. The water turns back into her regular form.

Tetramand Form
She lost two arms, but can grow them back. She also lost her strength, but each hand controls an element.