The boss designs are incredible, very cool! I like the environment pieces as well, though I wish there was a bit of visual feedback when you destroy the red blocks. Unfortunately, CTRL + D is the bookmark shortcut for Chrome (not sure about other browsers), so this was regularly interrupting the game when I had happened to press the combo as part of regular gameplay. For all of the bosses, I had a hard time getting one hit in without getting hit several times in the same moment, so that was a bit frustrating and made me feel like beating them was unnecessarily difficult. However, with some balancing and improvements to the collision boxes of bosses, the game could be a lot more playable. Good job!