Game is way too short. I thought it was a demo but it isn't marked as one, maybe this is a mistake? Either way there is less than 3minutes of actual gameplay here which is too short for a hack to be accepted.
There was one spot which I found extremely annoying. The section in the P switch palace where you pick up the shell as you are spinning. Since you are spinning the shell doesn't always go in the right direction which makes that part and everything afterwards very tedious to play. I think this one trick alone increased my playthrough time x10.
I did enjoy everything else that wasn't the shell part. If this was supposed to be a demo I'd recommend adding a few more levels and resubmitting it with that change in mind.