3 short but creative levels with different mechanics I all liked!
I hope you'll consider replacing your "switch" sound effect. This one hurts my ears.
I would liked to have seen very different art, or at least colors on the 3 levels indicating the mechanics of each are different.
I'd like to see you replace your brown kill blocks with something that looks dangerous. Dying from touching the brown blocks feels wrong. Maybe try lava or spikes! At first I thought I was dying from a game bug. It took me a while to figure out what was killing me.
It looks strange when the player appears inside solid wall blocks. I suggest trying to prevent this.