What an excellent game! The feeling of powering up was great (double jump, and the moment when I can kill a bat in one hit :) ) and the bosses all felt characterful even in such a tiny pixel resolution. You do a great job, in this and planet dark, of including cutscenes and phases that add a lot to a small game. When fighting the final boss, I really appreciated that it would "skip" you to the second phase if you had already gotten there, it felt like the game was respecting my time.
A bit of criticism because you seem like someone who takes that well: some of the platforming felt a bit finicky (for instance, getting bopped on the head by the ceiling which made me fall, or the roll timing feeling off). It was also hard to *feel* the stakes when I was at low health. One thing you might be able to take from Hollow Knight is the vignette effect at low health. I know it's hard making something in Pico 8 so I don't hold any of that against the game, but they are some spots I feel could be improved.
Thanks for making this!
[edit] forgot to say - great music and sfx!