Monsterween: Ghostly Horseman
Growing up in the Hudson Valley, I was always enamored with the Headless Horseman-- one of our more powerful and famous local legends. In our legend, it's the ghost of a Hessian soldier who was decapitated by a cannonball during the revolution. But most D&D settings don't have Hessians, or cannons, which means THE headless horseman never quite seems to fit into a tabletop game. Of course, the headless horseman also shares some similarities to the Irish dullahan, a headless horse-riding apparition usually described as a kind of fairy that foretells doom (and then causes it). And there are many more legends of ghostly horsemen in Europe.
In the belief that each ghost is at least a little unique, this week we've got a 5E statblock for a more basic ghostly horseman, to be flavored by the in-world legends and personality attached to it:
Bonded in Death. A ghostly horseman forms when a rider and their horse have a deep personal or magical bond, but the rider suffers violent death in a moment of intense emotion-- either on the battlefield in a particularly chaotic war or, as is sometimes the case, when a paladin and her bonded mount are lured into a trap while trying to live up to her oath. Until such a time as the spirit is banished, the two souls become inseparably intertwined, sharing in a nightly reenactment of the ride to the horseman's death.
Haunted Roads. A ghostly horseman haunts the stretch of highway leading up to her death, appearing to travellers who foolishly step out after dusk and attempting to run them down in her ghostly vengeance. Depending on the horseman's personality in life, there may be some holy symbol or other offering travellers can carry so as to escape her wrath. Regardless, like many ghosts, the boundaries of her haunting are clearly established, usually ending at bridges, gates or crossroads. If the horseman attempts to follow a traveller beyond her boundaries, she vanishes, returning to the underworld until the next new moon.