Jörmungandr

The Jörmungandr, also known as Omul Negru  or Romanian Boogeyman to the Upir, are an ancient and powerful race of winged, sulfur-based reptiles.

Origins
In Norse mythology, it is also known as the Midgard Serpent, or the World Serpent. In lore, there is only one Jörmungandr at a time and once it reaches its full enormous size it will encircle the earth until it swallows its own tail and when it releases its tail, the end of all things - Ragnarök - will begin. It is an example of an ouroboros, a reoccurring image within the Godfrey Institute and the white tower.

Appearance
Adult J örmungandr resemble giant winged reptilian creatures with humanoid faces and whip like tails,w hile infant J örmungandr resemble small white manta ray like creatures.

In Hemlock Grove
In the series, Jörmungandr are slight mix between the Norse Jörmungandr and the Omul Negru, or bogeyman. Omul Negru are invulnerable, shapeshifting, amphibious humanoids older than many races, even the Upir. The creatures ability to shape shift is due to it phenotypic morpho-fluidity, which allows it to change to a more human appearance, effectively disguising itself as a human, as well as possessing a human personality, consciousness, which can allow such as creature to attain genius level intelligence. Like Upir, they prey on humans, seemingly for blood, but possibly for flesh as well. They competed with Upir for food, but the Upir's bite was toxic to them and it allowed them to be defeated and seemingly made extinct. It also possesses enhanced strength, durability, and regenerative healing, the potency of which rivals, if not surpasses, an Upir's. If without a mate, the species can use female ova to fertilize, with the most plentiful and resilient being found in infants. With the right female ova, notably the one found in Nadia Godfrey, can then make more of itself, infecting humans with its young. The babies will grow inside the human, feeding off it until they hatch from the human's body, which kills the host. Meanwhile, the host will suffer dementia like symptoms and insanity due to their situation. Its sulfer based body is highly vulnerable to extremely high concentrations of nitrogen oxide, which can incinerate them. According to Upir customs, these creatures are a form of boogeyman. However, these creatures actually have the same relationship to the Upir as humans have to the Neanderthal, as the Jörmungandr are the race that proceeded the Upir and seemingly became extinct ever since the Upir species arose.

Connection To The Ouroboros
The Ouroboros is a version of the Jörmungandr myth a millennium year old story of a serpent cast into the  ocean by gods, then growing around the entire earth, to the point where it was biting its own tail. These creatures where meant to foretell the end of days, as it would become like a constrictor snake that crushed all like on earth into nothing.   Dr. Arnold Spivak, the last known Jörmungandr in existence,  used the Upir Virus to fulfill this myth, but for the species that followed his own kind, the Upir, while humanity remained seemingly unharmed by the virus. With the right female ova, notably the one found in  Nadia Godfrey, Spivak could create more of his species, infecting humans with his young at an infantile state. After consuming her, he would then be able to truly recreate his species, outdo the Upir that die off from infection from the Upir Virus, and potentially reestablish the species dominance on the planet.