In Iceland, New Year's Eve is Moving Day for the elves. It would be best to stay out of their way, but the very brave may try to use that as an opportunity to ask them what the future holds or receive treasures. Although, the ritual involves lying on the ground outside all night without falling asleep or moving, so it is often more dangerous than anything.
Encounters with elves can even be deadly at Christmas time, such as in the folktale of Hildur (who in some versions is a fairy queen but sometimes a Queen of the Elves). At her farm, a shepherd turns up dead every Christmas morning, and the cycle is doomed to continue until someone can break the spell.
Illustrations by Erik Forsman
This Swedish Christmas Carol, "The Gnomes' Christmas night", describes some of the actions of the tomten -from here.