Good game. I ran it on linux with wine and had no issues at all.
At the beginning it wasn't too easy for me to guess what my abilities did exactly. For example when I saw an enemy launch the spiked balls onto me I thought I'd be able to do the same and proceeded to ram straight into them. Also when I held Z for the first time and went into rainbow mode I thought that'd make me invulnerable for a short time (probably because it reminded me of an item in Binding of Isaac that had that effect) and also proceeded to walk into some spiked balls. It's not a big deal because I didn't die either time but it'd probably take just a couple more words on the floor make it easier, if you want to.
There could probably be some kind of "charging up" effect or animation when holding Z but before rainbow mode starts. Also it could be nice to have a different sound effect for taking damage and slamming into the walls.
You're probably aware of this already but a pause menu would be nice to have.
The outer part of the wall tile in the second world is too similar to the grass time to really look like a wall to me. It looks off especially for narrow walls like these ones
At some point in the second level something weird happened where my character sprite's scale got messed up and the pixels became rectangular:
I'd call them rixels but I think that's what people call rotated pixels already. I don't really know what caused it unfortunately, maybe slamming into the walls too much and/or going into the swamps. Anyway it fixed itself a couple rooms after.
Thanks for reading my essay, hope it's helpful.