The Fungi from Yuggoth — known to themselves, in the closest approximation human phonetics can manage, as the Mi-Go — are the only major entity in the Bureau's files that is definitively, unambiguously extraterrestrial in the ordinary astronomical sense of the word. They come from a planet. The planet is Yuggoth, which corresponds to what modern astronomy calls Pluto, though the Mi-Go's actual home is probably an installation on or beneath the surface of that world rather than the world itself, and probably also includes outposts on bodies not yet catalogued by human observatories. They travel between these places under their own power. They do not require spacecraft in the sense that humans understand the term. Their vestigial wings are not decorative.

The Bureau's working understanding of the Mi-Go is based almost entirely on the 1927 correspondence of Henry Wentworth Akeley of Townshend, Vermont, and on a small number of classified mountain-survey reports from the years following. Akeley was a retired folklorist who began noticing unusual activity on his farm in the wake of a local flood and who documented — in letters, photographs, and a wax cylinder recording that the Bureau still holds under tight access controls — the presence of a population of Mi-Go in the hills above his property. The correspondence was interrupted by Akeley's abrupt change of disposition in September of that year. Subsequent communications attributed to Akeley were, in the Bureau's assessment, not written by Akeley in any meaningful sense. The farmhouse was recovered. The farmer was not.

Physical Description

The Mi-Go are not neat to describe. They are roughly crustacean — the body plan is segmented, bilaterally symmetric, exoskeletal — but the exoskeleton is fungal in texture rather than chitinous, and the body shades pink to grey depending on ambient temperature. They possess multiple pairs of articulated limbs, some adapted for locomotion, some for fine manipulation, some for functions that appear to be sensory but do not map to any human sense organ. They have wings. The wings are membranous, vestigial-looking, and — this is the part the Bureau's physics consultants cannot explain — functional in the near-vacuum of interstellar space. They are not functional for atmospheric flight on Earth, which suggests that whatever principle governs their operation is not aerodynamic.

They do not photograph consistently. Every attempt to photograph a Mi-Go in normal light produces an image in which the creature is present but the creature's color is not. Black-and-white photography works. Color photography does not. The Bureau's imaging staff have no theory for this. Akeley's original photographs — black and white, taken with a 1920s plate camera — are the clearest images the file contains, and they are clear enough that the Bureau's zoologists have conclusively classified the Mi-Go as neither crustacean nor fungal nor any terrestrial phylum.

The Mining Operation

The Mi-Go come to Earth to mine. This is the central fact of the file and it is the fact that, paradoxically, makes them less dangerous than nearly anything else in the Bureau's archive. They are not here to destroy humanity, colonize the planet, or conduct ritual invocations of Great Old Ones. They are here to extract specific minerals from specific mountain ranges, and the presence of humans in those mountains is a variable they would prefer to minimize without going to the trouble of a confrontation.

The minerals in question are not on any human periodic table. The Akeley correspondence describes a substance the Mi-Go called by a name that does not phonetically render into English, which they extracted from deep shafts in the Vermont hills and transported — how and to where is unclear — back to Yuggoth or to one of their waystation outposts. Similar operations have been documented in the Himalayas (1938 expedition, partial recovery), the Andes (1954 Peruvian government survey, full recovery of equipment, no Mi-Go), and somewhere classified the Bureau will not name in this file because the classification predates the current security framework.

The operations are long-term. Mi-Go installations tend to persist for decades or centuries without significant change. The Vermont operation that caught Akeley's attention had, on the Bureau's best estimate, been running for at least eighty years before he noticed.

The Brain Cylinders

The one part of the Mi-Go playbook that is genuinely alarming to humans, and the one part that has earned the file its restricted classification, is the practice of brain extraction. The Mi-Go are capable of surgically removing a human brain from its body and installing it in a metal cylinder. The cylinder contains sufficient life-support infrastructure to keep the brain conscious, communicative, and — according to the Bureau's consultants — sane, for durations that are not meaningfully limited by the lifespan of the original body. A brain in a Mi-Go cylinder can, in principle, live indefinitely.

The Mi-Go do this to a small number of humans. Not many. The documented cases the Bureau has investigated number in the low dozens, and the selection criteria appear to be a combination of intellectual capability and voluntary consent. The Mi-Go ask. They explain the procedure. Some humans say yes, because the Mi-Go's pitch includes travel to places no unaugmented human body could survive, including Yuggoth itself, including the outer systems, including sites the Mi-Go describe with a specificity that suggests the description is not a lie. Some of the humans who said yes are still alive, in their cylinders, in Mi-Go installations, and they are — as far as the Bureau can determine — content with the arrangement.

Akeley was not asked. Akeley was taken. The distinction matters.

Cthulhu Wars Operational Note

Fungi from Yuggoth appear in the Cthulhu Wars miniature game as monsters in the Black Goat roster — the only faction whose roster includes them, though the in-game depiction is more overtly biological than the Bureau's case files suggest and the in-game role (as a cheap monster that primarily enables the Ghroth Action) is a game-mechanical simplification rather than a representation of actual Mi-Go behavior. The in-game Fungi are also much more numerous than the real operation appears to field. The Bureau is not certain why the Black Goat cults have adopted them as a unit type, but speculates that the connection is geographic — the same remote-forest regions where the Dark Young cults operate are adjacent to Mi-Go mining sites, and the cults may have struck some sort of local accommodation. The Shub-Niggurath file has more on this.