This is a very interesting concept, and seems to have quite a lot of potential to be made into a full puzzle platformer too! I really like the fact that you would pretty much need the ghosts to do almost everything, that really force you think in ghosts, and that's a good basis for a decent puzzle game.
My slight complaint would be there is almost no tutorialisation that introduce you to each of the ghost, thus making the learning experience a little bit more harsh. Also some levels are quite glitchly (the ones where you shrink into a small rock and roll), and it feels like it's not satisfying solving that puzzle (But we all understand shrinking and enlarging is quite an annoying thing thing to do nicely in such games). It would also be nice to have the ghosts reordered, so as to waste less time brewing ghosts.
But overall I enjoyed the game very much and hope this gets to be developed more! Well done!