As a rule, the lake sprits of northern Europe are monstrous and have nothing to do with the Fae, but there are exceptions to this rule, like thee Kelpies, Fuath, Glashans and Shoplitees.
Although these four magical beings have much more in common that their habitat, as they are all water spirits that take on the form of a horse when the need arises to go on dry land, the Scotish Kelpies and Fuaths take horse forms of giant size, while the Glashans and the Shopiltees show themselves as miniature waterhorses, when in the water, and as ponies when on dry land.
There are some other differences between Shopiltees and the Fuaths, most significantly, the Shopiltees are less bloodthirsty than their larger relatives, but that is because of their size, and not because a fundamentally different nature. As other water spirits of the north, the Shopiltee survives by drinking the blood of those who follow it to the water and drown, but because of their small size, they don’t need to kill as often as their larger counterparts.
The Shopiltees are said to be friendly and playful, but their playfulness is just a ruse to lure their victims, often children, into the water. Contrary to the Fuath, the Shopiltees never take on human-like forms, nor can they use force to overpower their victims, as the Nikur from Iceland, so to survive they depend totally on their luring charms.
Shopiltees were most common in the Shetland and Orkney Islands, but they haven't been seen in more than a hundred years.
-Arrowsmith, N. (2009). Field Guide to the Little People: A Curious Journey Into the Hidden Realm of Elves, Faeries, Hobgoblins & Other Not-so-mythical Creatures. Llewellyn Worldwide.
-McIntosh, A., & Inverness, L. I. X. (2005). Faerie Faith in Scotland. The Encyclopaedia of Religion and Nature, 633-634.