The Nykur

The Nykur is a shapeshifting water horse faerie that lures people onto its back only to run into a body of water and drown them. The sound of ice cracking over water bodies is said to be the sound of the Nykur's neighing. 
They hunt on the Southern Isles and the northern parts of the Eldre mountains. The only way to kill a Nykur is to put reigns made of Baken hide on them. Even then Nykurs can be wild and unpredictable and putting the reigns on them is extremely hard. All sea fairing people fear this beast. Since it can take many forms one can not always know that is a Nykur infront of them. So when winter comes you would be wise to stay away from large bodies of water.