Nice usage of theme.
Your gd.games URL is a bit messed up.
It was fun, I never managed to defeat the boss, the bird or me not sure knocked the red box into the wall and then I somehow got stuck between the buttons and the red box, so I basically just stood there and danced to the beats.
Audio was fine, a bit loud perhaps.
Graphics was decent looked like some fine programming art.
Would have been nice if the player turned upside down depending on gravity, so it would be easier to track, especially since sometimes it was a bit slow to start moving in correct direction.
Moving gravity to down always felt very strong while up was less so.
I got the feeling when gravity was pointing up that you dont clamp the up speed that is pushing on the player so when after a while I step off a ledge it just shoots the player very fast away with all the built up speed?
Good job!