The idea was exactly that. It is true that you don't necessary need to transform to stone to push the boulders; I should have made them heavier. It is also true that the air fan should not be able to lift the wood ball, Unity had a weird bug in the editor, and the "workaround" leaked into the build. The plan was to create more levels where different balls would be used to solve puzzles.
Thank you for trying it ♥