A small island lying isolated far to the north-west. Mountain Mass Island is unoccupied but is said to (and indeed does) contain buried treasures, presumably placed there because of its isolated location. An old boat crashed on this island a long time ago and the shipwreck still remains on the beach today.
The island, as its name references, consists of only a shoreline and a mountain trail. The mountain trail has several pathways which lead to treasure chests.