I love the angle rebounding puzzle aspect of the game, as well as the fact you have both BGM and SFX :D
It was hard to tell what would cause you to die. I feel like twice it happened to me without me being anywhere near the lava, but my guess is that if your boomerang hits the lava you lose? This could be made more clear, and preferably a little more forgiving. Redoing the early puzzles isn't fun when you already know how to do them and movement speed is relatively slow. Also since mouse can launch the boomerang, it'd be nice if the mouse automatically aimed in the nearest of the 8 possible throwing directions.
Still a quite fun game with a chill atmosphere. Great work!