Ahah, nice "ending".
I had a lot of fun! The game is long for a jam which is a good thing given each sequence is unique, and the difficulty was perfect for me (I think it took me something like 6 tries and 1h30, I also did a full second loop when I finally won ;) ). The intro is super cool and the game looks great. Controls and speeds are perfect and I like that the hitboxes of the spike traps and edges of the platforms feel at worst intuitive, at best permissive, the difficulty feels all the fairer. Finally I really like that you made a strong implementation of the theme.
NES Feel is perfect, which is why I don't mind adding a pedantic comment that I think that background parallax scrolling is a headache to achieve on an NES which would be consistent with the fact that none of the popular plateformers I can think of at the moment uses it.
I took a few notes, none of this is important but now that I took the notes I may as well share those ;) . When you die you need to refresh the page, as if you try to restart then the intro plays but then you immediately get back to the menu. When replaying I wish the intro was skippable. You also have to wait for the previous one to exhaust to take a cure again. Once again none of this matters though'.
Thanks for sharing!