Thanks for your comment! Happy you enjoyed it. I enjoyed creating it and might indeed take this concept further with more puzzles and unique bosses.
I also thought about adding a hard mode (you only have 1 heart) and a hardcore mode (if you die you need to start over) and a combination of the 2. Seems like some nice low hanging fruits to increase the challenge.
The boss is indeed 3D. I modeled and animated him in blender. In Godot I created a 3D scene with the boss, an orthographic camera at a 45 degree angle and a light. In my 2D scene I then added a SubViewport with the 3D scene as a child. Then finally I added a Sprite2D and used the viewportTexture to render the viewport to the sprite. Then the most finicky part was getting the hitboxes of the fists slamming the ground to align with where they visually were (due to the angle). For that I drew some path2Ds and made the hitboxes follow those paths based on the rotation of the boss.