https://en.m.wikipedia.org/wiki/Gr%C3%BDla

Grýla was not directly linked to Christmas until the 17th century.^[2] By that time she had become the mother of the Yule Lads. Terry Gunnell hypothesizes that the medieval custom of dressing as Grýla may be related to other visiting traditions^[3] such as Julebukk or the Yule Goat and that her name may mean “threat” or “threatening”.

She has the ability to detect children who are misbehaving year-round. During Christmas time, she comes from the mountains to search nearby towns for her meal.^[4] She leaves her cave and hunts for the children. She devours children as her favorite snack. Her favorite dish is a stew of naughty kids for which she has an insatiable appetite. According to legend, there is never a shortage of food for Gryla.^[5]