The arvidrone (/ˈɑɹvɪdrəʊn/) is a serpentine and limbless stranger which is black-skinned, black-fleshed, black-toothed, black-tongued, and black-blooded, this monotony of coloration broken only by the white stripes present on its underbelly and within its eye markings. It is slippery to the touch, and able to squeeze through any hole wider than a tin can in diameter. Its blood, though not caustic, does act as an irritant to any sensitive making contact with this fluid.
The arvidrone's flesh parts easily when sliced, but most cuts heal within seconds, albeit with a violent bursting of fluid from any abrasion. Though not flammable, the arvidrone does evaporate when exposed to high temperatures, first losing its elasticity, and then shrinking in size and growing brittle.
It is silent.
The arvidrone generates deep underground, with craggy natural gaps, long-sealed subterranean structures, and abandoned wells all being equally likely sites for infestation. It bubbles into existence from a black sludge, which coalesces in shape and grow more vivid in coloration over the span of several hours.
The arvidrone possesses a shyly sinister demeanor. A mature arvidrone travels through its environment in incessant sinuations, retaining no set territory, and backtracking only when dictated by necessity. Due to its elastic and compressible form, it most commonly spends the majority of its life in spaces too small for its bulk and shape to be apparent.
Interactions between arvidrone are infrequent.
The arvidrone is indifferent to human beings, as long as the sensitive does not make eye contact with the strain's eye markings. Once a sensitive looks into an arvidrone's eye, the arvidrone grows predatory1 in response.
A predatory arvidrone stalks a sensitive for seventeen days, neglecting its underground territory and instead, shadowing a sensitive just out of sight, keeping itself hidden in tight spaces or lying wait within the sensitive's location of residence. It always attacks on the seventeenth day, usually waiting until the sensitive is asleep, and devouring the sensitive in one swift, gluttonous motion.
The arvidrone develops an internal cavity in response to swallowing prey, its flesh parting and the inner lining of this structure growing thicker and more durable than its typical flesh. The arvidrone's inner cavity is not acidic, and in fact, exudes a not-insignificant amount of oxygen when making physical contact with a sensitive's body. As such, consumed sensitives tend not to die from suffocation, but instead die from the twisting and knotting motions of the arvidrone's body as it tangles itself in tight coils or forces itself through increasingly small spaces.
Although an arvidrone's body is not impossible to escape from, its slippery inner flesh poses an impediment to such attempts. Once a sensitive's corpse begins to decay, the arvidrone is quick to expel the corpse via regurgitation (or, occasionally, by forcing it outwards directly through its skin, these wounds healing up immediately afterwards). It is not poisoned by contact with rotting flesh.
All survivors of arvidrone attacks feel a compulsion to write the same 760-page document. This unnamed document consists of 170 unique words per page, with no word appearing more than once. This text, as a whole, does not seem to correspond with any known language, with any overlap between existing languages appearing purely coincidental. Survivors create this document from start to finish, taking breaks only to eat and rest. Upon completion of this document, no further compulsions seem apparent. Individual responses to the completed document vary depending on a sensitive's temperament.
As the arvidrone ages, it begins to travel deeper underground, squeezing itself into tighter and tighter spaces in order to reach these depths. As it does so, its body loses durability, with each tight squeeze forcing it to leave more of itself behind (and with no regeneration of form to make up for lost mass). It dies without announcement once it squeezes itself into an eventual dead end, its body, by this point, little more than a black paste that remains indefinitely, neither rotting, nor hardening.