Thanks for playing. It was really fun to see you play. As I was the only play tester, I guess some puzzles are much harder than I expected. That's why when you press ESC you can choose to skip a level.
Btw. In the level you got stuck on you have to push the top skull to the right, then jump down to the space right next to the exit and then drop the skull from the top, so it activates the button