Beautiful game, the controls are excellent, and I love the art style. The level design is good, and i didnt have much trouble finding my way through the level.
For Audio, I recommend you CheckOut BFXR(https://www.bfxr.net/), its a free sound generator for videogames.
also, in Nightmare mode level 3 I fell to the ground and didnt respawn.
Overall, Great Job :D
feel free to check out my game