Now that the goals of the Harbingers of the Yawning Void have been made clear, their leadership identified, and their followers established, it’s time to figure out how they fit into the campaign. Below are options to introduce the Harbingers of the Yawning Void as adversaries for your low-to-mid-level PCs. These can be single encounters or strung together to form a larger campaign against the cult.
Outbreaks of seemingly senseless and motiveless violence are causing unrest in the city. Young people are coming home bruised and bloody, refusing to tell their parents how they received their injuries. Overseers puzzle over laborers arriving late to work with black eyes and limping gaits. Soon after, a series of seemingly random attacks plagues the more prosperous quarters of the city. Reports of cloaked and masked figures attacking from alleyways, beating their victims, and then running away. At first, the city watch thinks it a rise in robberies, but often the victim is left with their coin purse and jewelry. When they are robbed, it seems an afterthought: the assailant grabs up something at the last second before escaping. Soon there are incidents of attacks on lone watch members by groups of assailants. The wealthy become suspicious of the poor. The lower classes are emboldened, some seeing the assaults as deserved reprisals on those who oppress them. The watch are caught in the middle as tensions rise, and the city seems poised to erupt in unchecked violence.
The PCs can enter into this scenario in a number of ways. They may be commissioned by an officer of the watch who believes the more unconventional approach of adventurers may uncover leads the watch cannot. A recent victim of an assault may appeal to them for aid. A cleric, having divined dangerous portents for the city’s future, could hire them to investigate. Or the heroes could simply be patriotic citizens who feel the need to help. Whichever route gets them involved, investigating will eventually lead them to a dockside warehouse where the Harbingers of the Yawning Void have instituted a secret conclave where people come to fight. These clandestine meetings supposedly provide members an outlet for their pent-up hostilities and tensions. The cult, however, is simply using it as a means to manipulate these people into stoking their aggressive tendencies. First, they fight among themselves. Then the cult persuades them to turn their violence on those who they feel have wronged them. If the PCs can infiltrate the place and defeat the Harbingers early enough, it may defuse the situation before riots and outright class warfare erupt in the streets.
A village is desperate for aid, believing the gods themselves have cursed them. First it was a string of accidents. Then a blight on the crops, followed by a disease that ran rampant through the livestock. Now people are getting sick. The locals are desperate, frightened, and angry. The local council seeks out the PCs to provide answers before the mob decides to string them up for their inability to solve the problems plaguing the settlement.
A cell of the Harbingers of the Yawning Void is behind the village’s troubles. The cultists, recruited mostly from local inhabitants—hermits, loners, and ne’er-do-wells—have been secretly heaping woe upon the village through various acts of sabotage. The latest problem, the sickness, is from pollutants dumped in the river from upstream where the cult is camped. Whether the PCs figure this out or track down the cult’s location from other clues left behind by the Harbingers’ machinations, they will have to locate the camp. Among the cultists there are one or two satarre infiltrators (see the previous entry for the Harbingers of the Yawning Void) as well as the evil cleric that leads this cell.
A town is decimated by invisible forces while they slumber. A small town awakes to find a portion of their population killed in their sleep with no signs of the killer save for the strange, twisted postures of the dead. The townsfolk were killed by a limbic eruption, a sudden release of poisonous gas from beneath a nearby lake that sits over an area of light volcanic activity. This is typically a rare but natural occurrence. However, in this instance, it is due to strange rituals conducted by the Harbingers of the Yawning Void in hidden caverns deep under the lake. The PCs may arrive in the town as the survivors are grieving and trying to make sense of the disaster. Or perhaps they were even in town when it happened. (You could require Constitution saving throws of the PCs while they sleep or simply assume they were strong enough to survive exposure or were even out of the area of effect, which is a portion of town closest to the nearby lake.)
Investigation is difficult, given that the gas has since dissipated. However, exploration of the surrounding environs shows a slew of dead animals in the wake of the gas cloud, leading to the lake. Magical divinations could reveal more. Alternatively, you could have one or more of the PCs suffer a wild, prophetic nightmare while under the effects of the gas, which reveals clues the PCs can follow. The cultists are still ensconced in their cavern lair, along with certain summoned elementals that were used to enact the gas eruption. Worse still, the leader has an old grimoire that describes the summoning of a herald of the void (see Tome of Beasts 2). It requires several mass sacrifices, of which the disaster in the town is but one. Can the PCs find and stop the others, or have they already been performed? Is the herald already on its way?