According to Scottush Folklore, Kelpies,also known as Each uisge (Eech-Ouska Scots Gealic for 'Waterhorse') are shapechangers, able to appear as a disheveled, wild-haired old man, a young, handsome, dark haired man or a sleek looking horse/pony with a black, white or grey coat. It's constantly wet, dripping mane betrays it's true nature.
Once on the horse's back the Kelpie gallops into the sea or loch to devour the victim, leaving only the un-touched liver to wash up on the shore.
I saw this particular waterhorse at a lake one midsummer, combining human and equine features, the pale of a corpse with bruise-purple hollows arounds it's pale eyes, it was the most malevolent fae I have ever come accross.