The Harrow
The Harrow is a roughly 1-mile diameter floating object that is used to collect souls for Taedra to torture. It is "piloted" by the demon Gaasiht the Harvester. Upon closer inspection, the "object" is actually a humongous mass of twisting, writhing, blackened bodies that are fused, chained, and stitched together in an eternity of pain. It floats roughly a quarter mile above the ground.
As The Harrow slowly makes its way across the landscape, it casts a cloak of darkness upon the ground below (equal to the Darkness spell). Nightmarish beings, lesser demons, tentacles, gnashing jaws, hands, crablike claws, and other horrors reach out from the darkness. The only sound that can be heard coming from The Harrow is a soft, steady, muffled heartbeat, which can be heard (and gently felt) about a mile away on a quiet night. As it draws closer the heartbeat is felt more intensely, and eventually the heartbeats of creatures with a few hundred feet fall into a synced rhythm with that of the abomination. In this way, The Harrow actually keeps its terrified victims calm, as their hearts are unable to race. This creates a mesmerizing, almost soothing effect on the victims, which makes it harder to run. Those who try find themselves winded very quickly as their slow hearts cannot provide fuel to their muscles quickly enough.
Anyone caught in the monstrous device's path is lost into the black shadow. Those few who manage to momentarily break free and run out are quickly sucked back in, in a manner that seems to be different for each person, based on their worst fears. Someone terrified of spiders will be jumped and hauled back in by giant spider legs, where someone else might be dragged back in by black sinister apparitions of an abusive relative.