Very fun game! I had a lot of fun testing the different pickups and what they did!
As a point of feedback, when I reached the boss, I knew thought something would spawn on the map that I would have to defeat. At first I couldn't find it and it took me a while to realize it was outside of the map at the bottom of the screen. Maybe adding an arrow pointing to the boss on the player's HUD could help? Also, it seems that the boss timer is not paused when the player pauses the game.
Anyway, I had a lot of fun with the game! Nice job!