One day, he just arrived...
He likes to make surprise attacks!
Sometimes, he shrinks...
But we are lucky to have an in-house Box Monster Whisperer. (If your home has a resident Box Monster, you'll sometimes need the services of a Box Monster Whisperer. Trust me on this.)
And just in case you were wondering where Box Monsters sleep, I'll give you a clue:
Not in their own bed!