This is a very good puzzle game but unfortunately the game bugged out at lvl 19. Mr Skeleton kept on telling me that the grey tiles could be pushed. So the dialog just kept looping around and around. Can you investigate this and see if you can replicate it. I just played through the game normally and got stuck on that bit of dialog.
Otherwise, I would have absolutely played your game to completion if it wasn't for that bug. This is a really cool and well executed concept for the 19 levels i got to play so thanks for sharing.
A few other small details, is that it isn't obvious i need to press Space to start the game. Also i think it would have been great is mr skeleton made a sound when he started to talk.