A Kallikantzaros pl. Kallikantzaroi is a malevolent Goblin in Greek folkore.
There is no standard appearance of Kallikantzaroi, but some Greeks have imagined them with some animal parts, like hairy bodies, horse legs, or boar tusks.
It is believed that Kallikantzaroi stay underground sawing the World tree, so that it will collapse, along with Earth. However, when they are about to saw the final part, Christmas dawns and they are able to come to surface during the winter solstice (from 25 December to 6 January). They forget the Tree and come to bring trouble to mortals.
Finally, on the Epiphany, the sun starts moving again, and they must go underground again to continue their sawing. They see that during their absence the World tree has healed itself, so they must start working all over again. This happens every year.
There were ways people could protect themselves during the days when the Kallikantzaroi were loose. They could leave a colander on their doorstep: if a Kallikantzaros approached for his evildoings, he would instead decide to sit and count the holes until the sun rose and he was forced to hide. The Kallikantzaroi also could not count above 2, since 3 is a holy number, and by pronouncing it, they would kill themselves.
Legend has it that any child born during the twelve days of the Saturnalia (17th through 23 December) was in danger of shapeshifting to a Kallikantzaros for each Christmas season, starting with adulthood. The antidote: Binding the baby in tresses of garlic or straw, or singeing the child's toenails.
In Greek language, Kallikantzaros is also used for every short, ugly and usually mischievous being.