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. It is highly recommended to purchase the Power Core Mk III and Air Drive upgrades for the Vacpack before attempting it.
- 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, and the location is unlocked on the map through the Map Data Node in The Moss Blanket; but the in-game map indicates that it doesn't belong to any existing biome.