Even though I made the game, I also never come far enough to hear the song fully kicking in. I thought that other web based platformer (like robot unicorn attack) are also fairly difficult for new players, so I didn't want to make it to easy. But maybe some kind of adaptive difficulty curve would be good. 

All objects have the same behavior, only the size in colliders is different. During playtesting I already noticed, that sometimes the player gets two jumps instead of one. Im not sure why this happens, maybe there are some invisible collisions happening, that give the player their jump back.

I note the feedback from you and the other commenter about wanting more jump control. Currently the jump range in x and y direction scales linear with the charge time. Their is an minimal and maximal jump lenght. Since the game started out as a runner theres also an invisible wall at abut 2/3 of the screen width. If the player passes this boundry the next jump will only move the player upwards and not forwards. Maybe thats whats causing the lack of control feeling.

Thanks for trying out my game!

Thank you for your feedback!
Its so cool to see people play my game. Im already thinking about a clever way to implement a charge indicator. Im not sure if a simple bar in the ui would distract to much from the gameplay. Maybe I should add an increasing amount of particle effects to the character to make the charge meter more cohessive to the character.

Thanks for letting me know about it, I should probably add some additional effects to the acid, to make it seem more dangerous.