A Doonie is a helpful road Fae.
The Doonie, Marvin Arcdael, stopped to help a circus caravan believing it was a road emergency, but it was a setup to kill him because he was also a Guardian and had a secret map tattooed on the inside skin of one of his arms.
The Dunnie, from Northumbrian folklore, is a small Brownie-like being in the folklore of the Anglo-Scottish borders, specifically Northumberland. The Dunnie has been known to take the form of a horse in order to trick a rider into mounting him before disappearing and leaving them in the muddiest part of the road. He also is said to disguise as plough-horses only to vanish when the ploughman takes him into the stalls.