In the best way possible: This feels just like a fan-made Earthbound boss fight. (Or Undertale boss fight, depending on how old you are.) You've gone and demonstrated that less is more by doing one scene very well. The effect for getting the attack timing just right is very nice, and there is a bit of strategizing to do even with only two options for the player on each turn.
There should probably be an epilepsy warning on this, but otherwise I think it's very good.
Nice work!