Skrat

The Skrat is a form of ghost from Scandinavian myth and a variation of the Myling. They toy with people at night, typically appearing at midnight and especially during the winter. They are known to hang on sledges and make the horses tired from the added weight. Once the horse is tired, the Skrat disappears while laughing. They have horse-like laughs and if someone finds treasure, the laugh of the Skrat can make it vanish. 

Citations:

Northern Mythology: Comprising the Principal Popular Traditions and Superstitions of Scandinavia, North Germany, and the Netherlands. United Kingdom, E. Lumley, 1851.