Moustache Island - also spelled Mustache Island - is a mountainous island located deep in The Slime Sea that is reachable from the Feral Phosphor section of The Dry Reef, by Jetpacking to a series of islands and going through a Static Teleporter at the end.
- There's a Blue Treasure Pod on one of the islands on the way to Moustache Island.
- There are no Gadget Sites on the island.
- The Island is located deep in The Slime Sea and is reachable from The Dry Reef, but the in-game map indicates that it isn't on the map, and doesn't belong to any existing biome.
- However, it is partially visible from Ring Island, and Ring Island is partially visible from Moustache Island.