I really like the character design here, but not the environment. Regrettably, you are using pixel art rather than vector, as your character uses, just inconsistent for me.
The music is lifting up the mood, nice!
Edit: The main problem is that when you are in the monster's dimension, you can't really see where the player's projectiles are (before, I set my screen's gamma and contrast too low, so I couldn't see enemy projectiles). You can make the player's color a little bit red when they get hit. The shooting rate was a little bit too low, and it's unconformable for me to click left again and again. It's better to hold left to fire.
The enemy's shooting rate was too high even though we could dash and be immune. What I like about the enemies is that they can avoid the player within a specific range. nice!