(The Greek Christmas Elves)
Greek folklore has it that there are little, evil, hairy creatures named Kalikantzaroi (trolls), that live in the center of the earth and all year long using a big saw they try to cut down the tree of life that holds/carries the world.
They are ugly and mischievous and they are afraid of the fire and the holy water. During the holidays between Christmas and Epiphany on January 6th these 'goblins' come up to the surface of the earth to bother and annoy people, playing tricks on them and causing trouble.
At night they come out of their hiding places to cause mayhem. They enter the houses through the chimneys the keyholes even the crackholes in doors and windows.
On Epiphany Day when the priests bless the waters and spray Holy Water they disappear immediately going back to the center of the earth only to find that the tree has fully grown back and they have to start all over again till next year!
These are stories grandmothers used to say to scare kids into behaving well during the holidays.