Adventure Time: Distant Lands (Demon Transformation)

Our thanks to Theultimatecrusader for recommending these scenes from the final episode, titled "Wizard City." The character Peppermint Butler undergoes a two-stage transformation into a demon/monster. The first stage occurs at the start of this clip. The second stage occurs at 0:52:

And here is the reversion:

In related news, we have fixed the link to our Adventure Time post from 2017, which featured a monster transformation.