I liked the different shell mechanics. I could see this being expanded upon to provide more challenges involving the different shells. Maybe even challenges requiring multiples shells at once to be used. The platforming did seem a bit tight at some points. In the Dash shell level, there’s a tight spot you have to dash into right before the end of the level that was difficult to get into.
Solid pixel art. The portal animation is particularly neat. I also like the UIs and title screen art.