This is an incredibly well implemented idea of the jam's topic.
I love that every world adds a new core mechanic and every level takes full advantage of those mechanics.
The game has a breathtaking pixel art, with a awesome soundtrack.
However, some levels in world 3 where ghosts appear are really difficult. It was so difficult, that i was about to quit, because with death you have to start the level again.
Despite that, i had a lot of fun playing your game and even made it to the final boss (I didn't beat him). Such a great game though. Amazing work, my respect!