Brag

From publisher blurb:

A brag is a trickster spirit that takes the form of a horse or donkey. It is fond of tricking unwary wayfarers into riding on its back before throwing the rider into a pool of water or brush, at which point it attempts to hold them down and extinguish the air from its victims lungs, similar to the kelpie. Survivors have also said the brag has appeared as a calf with a neckerchief, a naked headless man, and even four men carrying a sheet.