Nice idea about keeping balance: once you hit the wrong, you can heal yourself by going the other way.
One little thing is that the game could have hinted at how to win earlier; it is usually a bit of a bad idea to leave that vague. I was almost giving up, thinking it was "endless," before I saw the "solution ghost type." You could have had more ghost sizes and have the last one finally bring balance, etc.
Fits the theme well!