Fantastic pixel art for a game jam! Bosses were really tough as well lol. There's a few things I would change about the balancing. First, I would maybe make each attack slightly less frequent to give the player some time to run away or attack. Some of the attacks are also really hard to dodge, like the one where he shoots four particles at once with the blue one being the second from the bottom: It's impossible to time this properly since there isn't any variable jump height, and the player jumps way higher than the blue particle for him to deflect. My solution would either be adding some form of variable jump height or have him only shoot three projectiles rather than four.
I also found myself having a hard time with the controls. It feels really awkward using the space key with Z and X. Just make those few improvements and the game will already feel a lot better to play!