A brag is a creature from the folklore of Northumberland and Durham that usually 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 bush before running off laughing, much like the Bäckahästen (brook horse) or kelpie. The brag is also said to have appeared as a calf with a neckerchief, a naked headless man and even four men carrying a sheet. Some well-known brags are said to live at Picktree (where it was called the Picktree Brag[1]) and Humbleknowe.[2]
There is also another similar shape-shifter in Northumbrian folklore, the Hedley Kow.