I have noticed a little thing. There are 2 Buttons in the top left corner, but they both just reset the characters. I certainly think this is a mistake ^^
But I have a couple of ideas you could improve on.
1. I think a visual indicator, which button does what would be great.
2. I dont think you really need a heart system, because this way, I dont really care if the piece of paper gets hit once or twice ^^
I know this is for a game jam, so this way i dont really care about these small "problems", I just wanted to give you some feedback you can work with.
A solid platform puzzler with interesting mechanics. ★★★☆☆