Source: Mother of Flies, pg(s). 88f.
A vrykolakas is a form of undead born from the corpses of wicked people who committed crimes so terrible they were denied even basic burial rites. Related to vampires, these bestial undead can disguise their horrid visage magically to spread death and disease among the living, for even coming near a vrykolakas can infect a person with the plague. Their touch can drain the life force itself out of mortals.
A vrykolakas appears as a hunched, hairless, semi-intelligent ape-like creature with a withered humanoid visage and long fangs. Its pallid, pockmarked flesh is unnaturally stretched over its twisted frame. Since its spine is bent with undeath, the vrykolakas is rarely more than four and a half to five feet tall, and they weigh 20 to 30 pounds less than in life. However, the creatures possess the supernatural ability to disguise themselves sufficiently to pass undetected in the communities of the living, although not as their former selves.
Habitat and ecology
As undead creatures, vrykolakas do not possess a normal ecology, and they are solitary creatures. Newly arisen vrykolakas often seek their former family or companions as their first victims, seething with hate and resentment towards friends they only half remember.
Vrykolakas are very difficult to kill. If a vrykolakas is killed, its spirit immediately leaves its body and attempts to possess a nearby animal. If it succeeds, it returns to its grave and attempts to bury itself in the earth, rising within several days as a rejuvenated vrykolakas if undisturbed. Similarly, a person slain by a vrykolakas may rise as a vrykolakas within a few days unless they are interred with a proper blessing.
However, like vampires, vrykolakas possess a unique bond to their gravesite. Every Starday, the vrykolakas must return to its gravesite and rest buried in the earth and stones for one full day. While resting, the undead is helpless and can easily be destroyed, so they take great care to hide their burial place.