The 13 Horrifying Christmas Trolls Of Iceland
They leave the nice children gifts and the naughty children ROTTING POTATOES.
Officially called Yule Lads, these terrifying creatures visit the children of Iceland on the 13 days before Christmas. Children leave their shoes on the window sill and, if the child was well-behaved, the Yule Lads would stuff them with gifts. But If they were naughty, they stuff them with rotting potatoes. This is real Icelandic lore and you can learn more about it here.