Very well elaborated game! Upgrade system for weapons and mutations for the character. An interesting concept making the ways for combat also the means for exploration. In addition, exploring the cave is very challenging! It is, indeed, atmospheric! The soundtrack makes the whole experience more immersive.
Suggestion: the game is difficult! A lot of times I've been dancing in the spikes. Also, I don't know how much this would diverge from the initial idea, but how about a bigger dim light around the character? It would slightly increase the vision field, making things a little bit easier for the player.
Overall, its a gorgeous game, but it can be a brutal experience for the begginers. Well done!