King Acorn was a king of Mistmantle who built a playhouse along the cliffs for his children. The playhouse was abandoned for safety reasons, as the cliffs around it were starting to crumble and break away. Whittle told the circle about him and the play palace when they were looking for Furtle and Ouch in Urchin and the Rage Tide. It is unknown if he is a hedgehog, squirrel, otter or mole.