Ah, Underground Oracle Publishing venturing into monsters and creatures with Monsters Mythica: Kelpie. As a series, I cannot wait to see what lurks in the shadows. As for the Kelpie; by the Gods, what a terrifying sight.
The Kelpie myth has Celtic roots, and the inspiration for this monster has clearly influenced its design. It is endearing in its equine form, mysterious and inviting; and it's terrifying in its true form. The stat block is well balanced, although I would have loved if the myth's ability to shape change into human form remained, as a Large Fey foe, it is a formidable challenge.