Nice metroidvania! The pixel art is all uniform and well-drawn. I also thought that the sombre music fits the theme of the game well.
Narratively, it was really interesting to take control of the final boss at the end of the game. I liked how getting more HP helps in the platforming section of the game, but then makes the boss fight harder. Interesting balancing choice!
The controls could've used a bit more polish. The short-ranged attack is a bit too short-ranged (no pun intended), and I'm not sure I like the way the in-game jump behaves. It is also generally not a good idea to move the camera vertically on every single jump, as it can quickly get nauseating.
Nevertheless, this was a great game to play!