wow, great job! i really love the spritework here, and the theme is integrated very cleverly (even though i spoiled it by reading the questionnaire first... oops).
my big complaint is the keyboard controls--not sure if this is a standard set of keys i'm just not used to, but my hands had a hard time finding a comfortable spot (especially since i was using arrow keys for movement at first). i would have loved to use 'up' or 'w' instead of space for jump, and maybe a different key for the dash as well. i missed out on the slash move completely my first time through, but that's my fault for not reading the controls :p
the boss's invincibility frames lasted a little too long for my liking, but i still beat it (though i cut it real close!) so i guess i can't complain too much. i loved how the health got higher depending on how much you died in the beginning-- really neat stuff!!
if you keep expanding on this, i'd love more powerups (obvi) but maybe optional powerups, too? i feel like there'd be a lot of interesting risk reward with which powerups to grab and which to leave behind, so the final boss isn't *too* overpowered with everything, but you can also still get to that point without dying too much. but this is already real fun for a jam project! well done :)