Nice idea with the different forms. I liked how it was a clear progression, and there were clearly places that you'd be able to go later (foreshadowing).
Snail got stuck quite a lot, could use a smaller hitbox.
Some of the forms were seemingly unnecessary -- I spent a while trying to use the butterfly to fly around but couldn't seem to do so. I was hoping one of them would be able to walk on spikes or something similar.
When I fell off the level on some (all?) screens, it didn't respawn me so I had to refresh the tab.