Hey there!
What you’ve done with the boss is awesome—stages, movement, effects. I also love the mechanic with the “blank” bullets.
It just felt like you ran out of time. It would be really cool to fight not only the boss but also waves of enemies, and to have more control over buffs and extra damage (as PinoMatutino mentioned).
Great job, and thanks for the game!
P.S. I just read the other comment and realized the red bullets were critical, not blank :D