|Base Health|| 1000 HP|
|Base Damage|| 1000 HP|
|Found In||Moon Biome|
Upon the player picking up any fuel, S.A.I.L. will send the following message:
I am detecting entities attracted by the moon's erchius deposits. Their interest in you will grow as you collect more fuel. I would define these entities as 'intractably deadly'. I salute your fearlessness.
As the player collects more fuel in their inventory, the speed of the ghost increases. At approximately 3000 items of fuel in the player's inventory, the Erchius Ghost will move about as fast as the player running on foot. Dropping all fuel after receiving the message from S.A.I.L. will not stop the ghost from spawning and chasing the player. However, if, after dropping all fuel, the player quits the game and then resumes, the ghost will not respawn unless and until the player picks up a fuel item. Likewise, by beaming back to the ship and offloading all fuel, the player can evade the ghost.
Like other ghostly monsters, the Erchius Ghost is able to pass through solid matter. It is not susceptible to any weapons, and can't be delayed effectively. When near a player, the ghost's eyes will glow white and purple particles will emanate from the player to the ghost. Coming into contact with the ghost will instantly kill the player under virtually all conditions.
Erchius Ghosts serve as the limiting factor to how much fuel a player can mine on a single landing. Since they cannot be stopped or delayed, a balance must be struck between profit and danger.
Importantly, ghosts are able to move much faster when out of sight. As soon as they are more than about one screen's width away from their target, they automatically increase their speed, so that the player cannot get further away no matter how fast they move. This means that even very fast players cannot gain a significant lead in the chase. The ghosts always remain close enough to be a threat.
Players may consider digging out tunnels and escape paths before picking up fuel. The ghost only appears once Erchius is in the player's inventory, and is therefore not a threat before that point.
One method of evading the ghost is to only gather a small amount of fuel at a time, return to the ship to deposit the fuel, and beam down to the moon and continue mining. Another method is to terraform the moon, which will result in the Erchius fuel remaining, which can be mined without fear of the ghost, but this is incredibly expensive.
- When trying to spawn a Erchius Ghost using admin commands, it spawns an Erchius ghost that dies after a few seconds. This happens because the game gives a properly spawned ghost a specific player target. Without this assigned target, a manually spawned ghost's code crashes quickly.
- The Erchius Ghosts, Erchius Horror, and the Erchius crystals in general are implied to have a strong connection to the Ruin (or rather, extra-dimensionality in general), as SAIL states that the ghosts only started appearing after Earth's destruction, which involved the Ruin attempting to escape from its extra-dimensional prison.
- When playing with /admin mode enabled, the Erchius Ghost literally drains the color (really the life) out of the player.
- As the Erchius Ghost spawns below the player, it is possible to get the Ghost to spawn at the planet's core, at the lowest possible point. This causes it to get stuck with no health and repeatedly die, as touching the bottom of the planet will deal immeasurable damage to anything not in /admin mode.