Ghost Ship

Ghost Ships (幽霊船) are infamous derelict vessels that haunt the New World.

Background
Ghost Ships are vessels, that according to old stories by sailors, appear out of fog. Supposedly, they are ships that should have sunk, but sail once more on thin air, helmed by the undead.

Normally, they are encountered in areas that have large bodies of water such as the sea or a large lake. However, the one that originated from the Katze Plains is considered to be a unique case due to appearing so far inland without any large source of water body near it.

The Invaders of the Large Tomb Arc
When Heavy Masher encountered an Elder Lich in the Great Tomb of Nazarick, Gringham noted that there were stories about one elder lich who is commanding a ghost ship within the Katze Plains.

The Ruler of Conspiracy Arc
Whilst discussing with Pluton Ainzach on the Sorcerer Kingdom's intent to nationalize the Adventurer's Guild, Ainz Ooal Gown remembered about the reports of a mysterious ship traveling the Katze Plains. Ainz wanted to investigate the claims, so he could consolidate his control over the region.

The Paladin of the Holy Kingdom Arc
The Holy Kingdom Liberation Army had an encounter with a Ghost Ship. While traveling to the capital of the Sorcerer Kingdom, the delegation was engulfed by a blanket of fog. Out of the fog came a vast derelict ship that Gustav Montagnés identified as a ghost ship. Despite Remedios Custodio's insisting to attack the vessel, her adjutant convinced her not to do so, as it may warrant consequences from the Sorcerer Kingdom. His advice proved to be wise as it was flying the banner of the Sorcerer Kingdom.

The Half Elf God-kin Arc
It was mentioned by Ainz that the ship was acquired through the aid of himself, Cocytus and Demiurge when they went to the Katze Plains together.

Trivia

 * The arrival of a Ghost Ship is heralded by a thick fog.
 * As of now, it is unclear whether the Ghost Ship is a magic item, a unique undead monster or some kind of special summon.
 * In Mass for the Dead, the Ghost Ship was used an example of Ghosts existing in the New World, when a report came to Momonga that the Great Forest of Tob was possibly haunted.
 * In Mass for the Dead, the Ghost Ship's previous owner was slain by Igvarge and his team Kralgra. All the adventurers paid for the achievement with their lives, but the ship was later recovered by Nazarick and repurposed to assist in infiltrating a plot involving Six Arms and some rebellious nobles of the Baharuth Empire. To maintain that the illusion that the elder lich in command of the vessel was still alive, Momonga installed Iguva=41 as the new captain. And since then the Ghost Ship has been used by New Six Arms as it main form of transportation taking the workers on their missions or excurisons.