Not long after the first houses were built in the Glades, some of the workers and servants there reported sightings of a strange being in the forest between them, which they came to call "The Harthorned Shape". In the years since then, the sightings have continued, but the name has been shortened to "the Harthorn". What the Harthorn calls themself is uncertain; they've never been known to speak, only to appear in the distance and apparently watch. Thus far, while many servants, laborers, and visitors have reported seeing the Harthorn, they have never been seen by any of the wealthy owners of the Glades' manors. Some of these worthies consider the Harthorn a mere superstition of the lower classes; others believe their testimony that there is something out there; so far none has made a concerted effort to find the Harthorn or delve into its mysteries.

What the Harthorn actually is is a forestborn fey, an entity that arose from the collected élan vital of the creatures of the forest and that later assumed a more humanoid form in response to the human habitation in the forests. While they are still adapting to their new form and considering their ultimate goals, their main pursuit in the meantime has been to take lone and defenseless people they come across—wayward children, drunkards, people lost in the forest and faint with hunger and thirst—back to their lair, a pocket plane near the middle of the Glades, where they transform their captives into creatures of the forest to serve them. They do not do this often, taking on average less than one person a year, and the disappearances when they were noticed have been attributed to other causes; there are enough wild animals and other natural dangers in the forest that the occasional person going missing there is unremarkable.

The Harthorn appears as a pale humanoid figure of indefinite gender, with large, slanted eyes in a narrow, pursemouthed head. Their head bears two large cervine horns that gave rise to their name. The Harthorn gives off a faint glow, barely perceptible during the day but much more noticeable at night. They appear at a glance to be wearing long, thin white robes, but at a closer look the "robes" are billows of mist rather than fabric.