On level 5, 6 and 9, there are stars inside a small box. I find it difficult to fit the player (before combining with anything) into the box. Is it intended for the star to only be reachable after getting a certain shape?
On level 5, that's a collision bug, the "easy" way to get the star is to land on the floor above it, then do left/right quickly to fall towards it
Level 6 is intended to be taken when you've reached your final form, and on level 9 you just have to jump up as soon as you spawn, but if you move around, it becomes very hard :p