Good game, I liked it.
in the boss fight, At first I though it's the strings getting down from screen is having something to do with gravity flipping and i somehow hurting the boss, but it was just the bullets.
A tip I'd like to say, whenever you're have a switch mechanic (on/oof gravity),try making it in a one button would be best, also don't put the apples on the spikes >_< haha..
Good work with the assets , congratulations of your game! ^^