The Interloper

The Interloper, also known as the Firstborn of the Wood, is a creature found in Appalachia.

Background
The only direct mentions of the Interloper is by Jeff Lane in recorded holotape messages and cultist notes. In the messages, Lane describes the nature of the Interloper's "calling" to himself and other members of the Cult of the Mothman. The Interloper is known to have communicated with the "First Priestess of the Wood," an honored individual who conveyed the creature's messages to the cult's followers. The Priestess appears to have been placed into the coffin behind the lectern in the main cultist shrine.

While previously just a "false memory," the creature's existence was confirmed to Jeff Lane after hearing a tale of the entity "made real" deep underground by a mad storyteller. It is at this point at which Lane describes the Mothman to be merely a creature, more similar to the human race than the Interloper and the "unknowable horrors" hidden within the subconscious mind.

The creature later calls to Jeff Lane in a lucid vision, inviting him deep into the depths of the Lucky Hole Mine. He explains how that although it appears others have also heard the Interloper's call, the entity summons him alone in the end. Lane further states that the Interloper chose him as the "conduit of the unknowable" and how the "hidden reality" will finally become revealed.

According to the series of notes spread throughout the mine, supernatural events occurred as the cultists inhabited the location, including the formation of a water spring. The creature will bleed if struck by the player character and its tentacles occasionally move, indicating that the creature is still 'alive', despite is apparent dormant state.

In 2103, a sect from the Cult of the Mothman congregate within Lucky Hole Mine and continue their zealous worship. They kneel before the Interloper with arms raised high, offering human sacrifice and blood-filled jars to the Interloper.

Characteristics
The Interloper is an immense, dormant creature sprawled in the depths of the Lucky Hole Mine. It appears as a multi-armed humanoid-like figure consisting of a vine or root-like material. Writhing, tendril-like appendages emerge from its gaping maw and stretch across the floor. Multiple quivering, disfigured arms protrude from the creature's back, ending in tensed, grasping hands. When hurt, a shadowed blood will appear. The Interloper emanates an eerie, droning hum and allegedly possesses supernatural abilities, including telepathic communication and alteration of nearby terrain. A low hanging fog surrounds its body, as well as several skeletons, corpses, and effigies.

Appearances
The Interloper appears only in Fallout 76.

Behind the scenes

 * The Interloper may be a reference to H.P. Lovecraft's works, especially pertaining to the Cthulhu Mythos and "The Dunwich Horror."
 * The dormant nature of the Interloper is a nod to the Call of Cthulhu phrase "ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn," meaning "In his house at R'lyeh dead Cthulhu waits dreaming."
 * Similar to Fallout 4's Dunwich Borers, statue reliefs of a face populate the area, albeit in a higher volume. These "buried statues" might be a reference to another of Lovecraft's stories, "The Shunned House," in which the protagonist digs underneath an abandoned haunted house, only to uncover the elbow of a colossal creature buried underneath.
 * The game files define the creature as an actor mesh and designate it "gutpuker."