The Scandinavian Nisse is rumored to be a small, gnome-like being. They live in barns or farm houses, or in the nearby woods. Nisses are excellent at hiding and can sometimes turn invisible - you'll only ever catch a glimpse of them (if that).
When treated with respect, a Nisse will protect your farm and even help with chores. They are especially fond of animals. But beware: a Nisse who feels insulted or disrespected can turn mischievous, even vicious.
To this day, it's tradition to leave a bowl of porridge in the barn for the Nisse on Christmas Eve. I didn't grow up on a farm, so my mom had us put a bowl out in the garage instead. Just in case.