Forbidden Island is a large island lying in the lake of Fusion Matter between Marzipan City and Stormalong Harbor, the only platforms being several heavily damaged docks and sunken ships. The island is surrounded by a damaged fence. There are also a damaged cabin and a crashed S.C.A.M.P.E.R. The only major NPC here is GIR, but there is also the stranded S.C.A.M.P.E.R. pilot, Numbuh 6934.
The S.C.A.M.P.E.R.'s crash was the result of a malfunction caused by GIR. Apparently, when GIR was taking a ride in the S.C.A.M.P.E.R., he pressed a red button which released the engine from the ship, causing it to crash onto the island, and standing GIR and the S.C.A.M.P.E.R. pilot there.
Fusion GIR's lair lies to the north of the main section of the island, which lies partly inside the Shipwreck Infected Area.