Hastalÿk is a Great Old One in the Cthulhu Mythos. Its only appearance is in Chaosium's supplement Malleus Monstrorum for their Call of Cthulhu RPG.
Description[]
Hastalÿk is a gestalt entity composed of millions of microbial parts. It sweeps from planet to planet, amplifying and altering existing contagions as well as causing cellular mutations. It is neither a disease nor carry any disease, but a "mutating force" that forces native species to mutate uncontrollably, enabling diseases to spread throughout the planet.
Humans who caught a disease mutated by Hastalÿk may experience delusional fevers or fevered visions and dreams about other cosmic horrors. In rare cases, their body and voice may be possessed and controlled by Hastalÿk or another Old One.
Not much fact is known about Hastalÿk, only conjectures from scholars and scientists. Whether the mutation and spreading of disease are its goal or only side effects of its presence, as well as whether it moves throughout the galaxy or actually spreads itself on all worlds while remaining dormant on most, are highly contentious. A few scholars even suggest that Hastalÿk's consciousness may be active in many locations at once with varying scopes, thereby causing either global or only local outbreaks.
Interaction with Hastalÿk is difficult because its thoughts are beyond human comprehension, though it might be possible with advanced species such as the Mi-Go.
Worshipers[]
There are no known organized human cult of Hastalÿk, only certain affiliated groups or individuals exist that want to summon Hastalÿk to Earth to serve their own goals.
In the Mythos[]
Some researchers claimed that Hastalÿk was responsible for accelerating certain outbreaks on Earth, such as the 14th century's Bubonic Plague or the 20th century's Great Influenza epidemic.
When a Great Old One awakens, Hastalÿk could potentially be awakened as well, mutating nearby life forms to better serve the Old One.