The monster shouldn't have done that. Of course the castle walls weren't strong enough to stop such a big monster, but it didn't need to prove it. And, come on, rebuilding isn't going to make this any better.
He'll get over it. He always does. For now, he throws the pillow walls around the room, which scares the cat, but there's no need to scold him because he's right about this one.
"Monsters don't think first," says the monster in a monster voice. But the monster has already transformed; the voice is false and out of place.
A snack helps, sort of. It's hard for him to swallow the chunks of granola bar while he's still sniveling.