Very good and responsive platformer!
The art is very cool, reminds me of Edmund McMillen's games, like Super Meat Boy and The End is Nigh. The passage through the different layers itself reminds me of The Binding of Isaac. I really like how the music changes and sets the tone of the level.
I think the game would do well if the camera responded more actively to the player's movements, since when using jumping platforms, the player's character flies off the screen, and he becomes exposed to hazards that we do not see. So, I died several times from flying skulls, into which I was shot by a spring.
It would be nice to more clearly display the hazard with shooting projectiles on the 4th layer. I saw 2 projectiles, dodged them, and then on the platform above I was shot right at. You could put a barrel to show the source of the hazard. It's pretty funny that the random generation on the last successful run generated it in such a way that I didn't need to cross these projectiles.