The Rock Wall Thief is a character who appears in the episode "City of Thieves." He steals Phil's pajamas and wears them as some sort of a cape, then sinks back into the wall. He has a high-pitched voice, but he only laughs. He later appears as a toy in "All the Little People."
The Rock Wall Thief's body is made of cobblestone. He has a tough right arm but a skinny left arm that is lower on his body. Each hand has only 3 fingers, and his feet do not have toes.
He can phase in and out of stone walls like the Hag can with trees and wood.