Great cinematics and very nice tutorial. Got the reference from "That one game we know".
Great level design! The boss design is also really good, and its attack mechanics are varied and interesting.
However, I do think some of the attacks feel a little unfair. When the boss gives the attack signal, the attack happens almost immediately. A good solution would be to use different visual or sound cues to indicate which attack is coming, followed by a short delay before it happens. This would give the player a better chance to react.
Overall, great work! I really enjoyed it and stayed hooked on the boss fight for quite a while.