Oh dang! After the cute potion-making game I wasn't expecting this one to go so hard! Incredibly effective storytelling--the breathe in, breathe out motif works really well. Great use of text effects and screen effects (but not so much that they're distracting), evocative art, and THAT SPECTACULAR TRANSFORMATION ANIMATION. And it's just a good story--the character's perspective and unreliable narration works powerfully. You're batting 1000 in my book.
I might just shorten the conversation with Jessica a lot, since she doesn't turn out to be important, but that's really the only thing I would change.