(Music: Song of the Water Kelpie (Manx Trad))
Kelpie is a shape-shifting water spirit inhabiting the lochs and pools of Scotland. It has usually been described as appearing as a strong black horse, but is able to adopt human form. One of the Kelpie's common identifying characteristics is that its hooves are reversed as compared to those of a normal horse and it's also able to extend the length of its back to carry many riders together into the depths. Kelpies take their victims into the water, stoke or even devour them.
Usually the legends about Kelpie tell us about several children clambering onto the creature's back while one most cautious child remains on the shore. He then pets the horse but his hand sticks to its neck. In some variations the lad cuts off his fingers or hand to free himself. He survives but the other children are carried off and drowned, with only some of their entrails being found later.
Such stories served as a warning keeping children away from dangerous stretches of water.
Another sign of a kelpie is their hair - despite their form, their mane consistently stays wet and entangled with river weeds. Which is why, to disguise this, they are usually found around lakes, ponds and other quiet places with deep water.
There are also some legends claiming they can shapeshift into creatures other than horses and humans. They usually stick with the former forms though because they are the most inviting and the easiest way to lure victims to their doom.
Scottish lore is so fascinating :)