Fullmoon Island is a very small island west of Newmoon Island and south of Canalave City. It can be accessed by talking to Sailor Eldritch who will take you to it by boat. Newmoon Island, which is the nearest location to the east, appears to be a mirror image of Fullmoon Island. This theme of mirroring between the two locations can be seen within the names of the Islands, full moons are the end of a lunar cycle and new moons are the beginning, as well as the Pokemon who are encountered on the islands, Cresselia and Darkrai being known counterparts/rivals. As well, Darkrai causes nightmares, while Cresselia is said to be able to cure people of nightmares, or give joyful dreams.
In the games, you go to Fullmoon Island to get the Lunar Wing from Cresselia for Sailor Eldritch's son. Eldritch's son had fallen into a nightmare state and could only be cured by the Lunar Wing, which is dropped by Cresselia when you first encounter it on the island. Afterwards you can return to the island and encounter Cresselia again, after which she becomes a Roaming Pokemon whom you will be able to capture upon finding.
The only purpose of Fullmoon Island after completing the Cresselia/Lunar Wing arch is that it's the only way to access the northwestern most part of the Sinnoh Underground.
Fullmoon Island · Newmoon Island
Place of Interest
Valley Windworks · Fuego Ironworks · Galactic Eterna Building · Hallowed Tower · Lost Tower · Solaceon Ruins · Galactic HQ · Great Marsh · Spear Pillar · Snowpoint Temple · Sendoff Spring · Hall of Origin · Canalave Library · Flower Paradise · Seabreak Path · Distortion World Pt · Iceberg Ruins Pt · Iron Ruins Pt · Rock Peak Ruins Pt
|Kanto (Sevii Islands) · Johto · Hoenn · Sinnoh (Battle Zone) · Unova · Kalos · Alola|