Thanks so much! The gray blocks were intended to be figured out on your own, since the level that teaches them has very little moving parts but no other possible solution. But I know now that it wasn't clear enough, since you're not the first to point that out. Thanks. Maybe I should've done like I did with the main mechanic, a level that forces you to use them accidentally.
You were very close to the end, you had to solve that level and 2 more. That's where the really hard levels start (we made the last ones thanks to ideas coupled with accidental discoveries, so to be honest I don't think I would be able to solve them if I hadn't made them). You can check the video in the description if you want to see the solutions!