Is called a Cosroom, turns Maryo into Cosro. (See 2. .) Looks like a mushroom with a clear astronaut helmet.
Maryo turns into this form after he eats/picks up a Cosroom. Cosro can shoot with his pistol. Is shoots at a possible spot. The spot is chosen by clicking on it. It takes 3 hits as default for Cosro to turn back into Maryo. He can also destroy Cosicks (See 3. .) by clicking on them.
The block is called a Cosick.
They can't be gone through in any way. The only way to get past them, or, well, destroy them, is by shooting them as Cosro.
They look like black glass with space-like spots on them.