The callicantzaros is a Greek vampire which attack people and tear them up on the holy days between Christmas and Epiphany.
According to Christian Greek folk belief, a child born during Christmas (Dec 25) and the Epiphany (Jan. 6) will become a callicantzaros. The callicantzaroi are also active as a threat to normal humans during this same period of twelve days.
They often appear in half-human, half-animal shapes and are active during the time from the beginning of Christmas to New Year's Day. They roam the countryside and enter villages at night but sleep in caves during the daytime. At the end of this period, they travel down caverns or other tunnels to Hades in the bowels of the earth. While on the world's surface, a male Callicantzaros is apt to kidnap a mortal woman to bring her back with him to the underworld as his bride and have children with her who also became callicantzaroi.
It was said that the first victims of a callicantzaros whose parents were both mortal were often his own brothers and sisters, whom he was apt to bite and devour. To prevent an infant of two mortal parents born during the proscribed Yule Tide season from becoming a callicantzaros, the infant was sometimes held feet down over a fire by one of the parents until the toenails were singed.