I thought the concept here was really neat and not a mechanic I've really seen before in a game like this. Also a nice variety of enemies for only having a few days to work on it.
I think a piece of feedback I'd give is just adding some acceleration/deceleration to the skull to give it a little extra juice. It always moving at a standard speed felt a little odd. Also a bit of invincibility frames after getting hit would help. I kept getting killed by the gaggle of ghosts all hitting me at once.