There's an empire, and the empire borders a titanic Forest. Things come out of the Forest, horrific and monstrous things. The PCs are one of the teams of warriors known as WitchHammers that patrol the border with the Forest, protecting villages and towns, hunting down monsters, and hunting down the Witches (basically anti-PCs) who create and guide these monsters.
A varied and hard bitten lot. The job consists of long period of boredom broken by occasional bursts of extreme danger and terror, so most people usually put their talents to work else where. As the name implies, WitchHammers fight Witches and the Monsters that Witches create. Witches come from the Forest, which is a dangerous place.
Witches are the unfortunate people who go into the Forest and are not killed by the Forest. Instead, they are transformed. Their minds are broken and malicious, their bodies are riddled with mutation, and their spirits can wield a part of the Forest's power in order to destroy and corrupt other beings.
Witches vary widely in their physical form. Some are dwarfish, with shriveled arms and the legs of lions and a dozen raven wings about their body. Others are immense, with slug like bodies the size of an elephant, and rows of insectile arms. Some witches are strikingly handsome, others are terribly foul. Similarly, the behavior of Witches varies widely. Some will dart into the border lands, kill a single family, and then flee back to the Forest to hide for years. Other Witches will go on mad crusades, traveling ever deeper into the Empire until they are brought down by the massed crossbows of a battalion. Some Witches skulk in the groves and fields, calling shadow hounds to lay siege to a village at night. Some Witches create massive undead constructs out of the leavings of graveyards and then lay waste to a village at noon-day. Some Witches use mutated rats and virulent disease, others bring with them malign spirits, hauntings, and killing dreams.
What all Witch have in common:
Witches are malignant. Any spark of decency in them was snuffed out by their transformation.
Witches are cancerous. They have an innate understanding of magic, and for them creating and corrupting with magic is like eating and breathing is to a normal human. If given free reign, Witches will endlessly craft and breed additional malignant creatures and servants, and infect normal humans with their corruption.
Finally, Witches are deadly. Witches radiate an aura of fear and terror. Their bodies are fast and resilient, and their minds have a mad cunning. A Witch often has a strength out of all proportion to its size, and a magical power to rival any human sorceror.
A monster is the general name given to any of the creations of a Witch. Monsters can be anything between a mosquito made out of shadow that suck slightly more blood than usual, to a gigantic elephant made of living flame that petrifies everything it looks upon. Monsters are rare in the world, and most citizens of the Empire will never see one.
As a general rule, monsters are terrifying. They do not move like terrestrial creatures, and they radiate fear, terror, and wrongness. The most common reactions to a monster is to cry, run, hide, or simply freeze in place. Even veteran soldiers have difficulty standing and fighting against Monsters.
The Forest is dangerous. Really really dangerous. You might not die if you go in there, but if you stay there long enough or go there enough times you will die. The Forest contains wonders and horrors, and it is likely that the greatest of these leave no witnesses. Sometimes the Empire gathers the force to take a chunk out of the Forest, and sends in an army of woodsmen protected by an army of soldiers to rapidly clear cut an area. Once the trees in an area have been cut down and burned, the hostile aura of the place dissipates. The Forest is gigantic, and the border between Forest and Empire stretches for many hundreds of miles.
The Empire is a gigantic state with far flung provinces, bustling cities, armies, wars, trading houses, a state religion and priesthood, many many branches of civil service, and a succession of emperors appointed by its patron-deity, Sai-ias. Given that it is mostly comprised of humans, it's a pretty stable, well run, and just place. Most of this won't affect the WitchHammers though since their business is on the Frontier.
A large and nebulous area where the Empire borders the Forest. The irregular border between Empire and Forest stretches from SouthWest to NorthEast for ~five hundred miles. The depth of the Frontier varies depending on who you ask, but the area is generally characterized by A) the newness of the settlements, B) much lower population density and less development compared to the civilized heartlands of the Empire, and C) the danger of attacks by monsters and Witches.
The actual development of any area on the frontier depends on any number of factors, from the fertility of the land and the value of the resources, to the number of attacks, to the vagaries of population movement and settlement. The population on the Frontier is varied, and like the WitchHammers it tends to consist of people who had some reason for leaving the more civilized lands to the West. You have transported criminals, migrants looking for new farm land, communities of people that had religious, ethnic, or clan-based feuds that they are hoping to leave behind, individuals who had some sort of history they are looking to leave behind, merchants looking for new trading opportunities, researchers who hope to study the unique properties of the Forest, and people who don't much like other people and don't want to live too close to them.
Villages are usually about half a day away from each other, and have 100-200 people. Towns are usually about 2 days away from each other, and have ~1000 people. Large towns are usually about 4 days away from each other, and have ~4000 people. Most bureaucracy takes place in large towns, ditto with where the large garrisons, religious orders, etc. are located. Further west and away from the border there are larger and more civilized towns.
Most of the Frontier consists of land that was reclaimed from the Forest at some point, i.e. it was clear cut and the undergrowth was burnt. So the terrain tends towards grasses, wheats crops, stuff life that. People on the Frontier are highly suspicious of trees, and don't let them grow too large of in clumps of more than 3 or so.
Religion: The official state religion is the worship of their patron deity, Sai-ias. It is typically depicted as a large, golden, many-legged sun. Many citizens follow this religion, to a lesser or greater degree. The primary values of the religion are rationality, peace, forgiveness, and the careful development of one's own potential in the service of the Empire. Full priests of Sai-ias are relatively rare, but they have miraculous powers and even been know to raise the dead. When needed these priests can also command immense temporal resources. Even in civilized areas they will have at least 20+ veteran guards traveling with them. Their are a host of lesser religions, but they have difficulty in consistently producing miracles which makes proselytizing more difficult.
The Army: In charge of forts and garrisons along the Frontier. The Army can summon large numbers of troops to deal with major threats. This happens slowly though, and is often not sufficient to deal with quick incursions by monsters or Witches. Another difficulty for the Army is that it is difficult to train people to be heroes. So they often have problems with motivation, where squaddies are reluctant to venture out into the night in order to hunt/be hunted by unnatural abominations. Many a village has been devastated while its protectors huddle behind stone walls.
Merchant Houses: Major economic and political players in the more civilized and densely settled West. They do not have major interests on the Frontier, but occasionally they become involved because of overseeing their investment in some new project or simply from travel and sight-seeing. Major Houses include House Buspar, House Forteo, and House Toradol.
The first and most important characteristic of a WitchHammer is bravery, and the ability to directly face supernatural terror. The natural reaction to a Witch or a Monster is to run away in stark, raving fear. These creatures give off an aura of terror and utter wrongness. When faced with a monster for the first time, most people will be completely paralyzed by fear or else will immediately flee or will be entirely paralyzed with fear. Those that can act will often be hesitant or panicked in their decisions. The WitchHammers have learned to overcome this fear and fight decisively against supernatural foes. For some WitchHammers, this bravery is the residue of dozens of hard-fought battles and a life of grueling challenge. For other WitchHammers, this bravery comes from a fierce dedication to a cause or from some burning drive. For still others, this bravery is merely a symptom of insanity, and an inability to normally process fear or emotion. In any case, every WitchHammer must be brave.
The Wagon is one of the less well known but still vital weapons of the WitchHammers. This oversized and finely constructed vehicle stores the myriad weapons and tools that the WitchHammers need for their missions. A typical Wagon has iron wheels and an iron barred frame, and is an extremely sturdy (if bumpy) ride. It is constructed to hold hundreds of pounds of equipment, as well as to act as a holdout of last resort in case of attack. A well-stocked wagon also has dozens of reagents, filters, herbs, and chemicals. When a WitchHammer passes or retires, his equipment is left with the Wagon and becomes part of the communal property. If none of the WitchHammers return from battle, saddened villagers will usually return the forlorn Wagon to the nearest town or WitchHammer academy in order to claim a minor reward.
The collected and collated knowledge of Monsters and Witches is known as the The Hammer of Witches. Confusingly, this is often shortened to simply the "WitchHammer". The full and collected volumes of the WitchHammer weighs several hundred pounds, and copies are usually kept well back from the front lines. WitchHammers on the Frontier occasionally carry a smaller and more condensed version of this book for reference. After battling a Witch or Monster, the Witchhammers will usually give a report to their local chapter, so that their observations can be added to the recorded store of knowledge.
Despite the chaotic nature of Witches and Monsters, the WitchHammers do keep detailed records of their past encounters with the foe. They have yet to find a single Witch or Monster that is exactly like any other, but if the monsters do not repeat they do at least rhyme. These centuries of records are often studied by new WitchHammers to give them an idea of what they might face in battle. More cerebral members of the Order study these records to see if they can find some underlying pattern or reason behind the Witches, but despite a long history of theory and debate, they have not come to any absolute conclusions.
Some WitchHammers are brought up and trained in special academies, before being apprenticed to more experienced WitchHammers in the field. Other WitchHammers volunteer in cities, or are recruited on the Frontier to replace losses sustained while on patrol. Those who join the WitchHammers are generally tough, tough minded, intelligent, and physically fit.
The WitchHammer's are one loose branch of the Empire's government, and are provided with a stipend that covers daily expenses, inns, reasonable food & travel gear, etc. The organization keeps offices in large towns, so every few months a WitchHammer troupe will circle by to pick up their stipend, claim bounties, etc. Larger costs (e.g. replacing a lost donkey or wagon) can usually be reimbursed to, so long as their is a reasonable excuse and the team is in good standing.
Proof of killing a monster is worth 100G, though sometimes for truly fearsome abominations the bounty goes much higher. Killing a witch is worth 1000G. The bounty is usually claimed through a "Witch Heart" a gray and jagged stone that is invariably found within the body of a Witch.
Successfully killing a Witch is worth somewhere between half a level gain to a full level gain. (depending on what level your players are, and what rate you want to advance things) Defending a town/fighting Monsters, but not killing the Witch who is behind it all, is worth 0.25 to 0.5 of a level gain. (again, according to taste, at the moment I'm going for a shorter and faster campaign)
Sometimes WitchHammers meet foes that are too difficult for them. Sometimes WitchHammers meet foes that are far, far, far too difficult for them. In these situations it is understood that they will save what people they can, retreat, and spread the news so that a larger and more powerful forces can be marshalled to meet the threat.
One of the draws of being a WitchHammer is the retirement plan. If the PCs manage to kill 5 Witches and turn in their Witch-Hearts, the Empire will reward the PCs with massive wealth. Specifically, the successful WitchHammers are each given a golden bust of their own head. This piece of pure gold statuary is of immense value, and allows them to retire and pursue basically any goal they might want (buying an estate, starting a business, never worrying about money again, etc.)
From the Empire's point of view, this serves to A) reward success in a very visible and memorable fashion, drawing in fresh recruits to the WitchHammers and B) is a nice way to put WitchHammers out to pasture before they are exposed to too much of the Forest's corrupting magic. The longer that people fight the Witches and the Forest, the more opportunities there are for them to be infected by its magic and become monstrous themselves.
About 3% of WitchHammers make it to retirement.
Besides the WitchHammers that are out patrolling the Frontier, there's also a solid support structure which provides the supplies, weapons, training, HR, research and education, and the 100 other things involved in keeping a large organization running. Many of these people are former WitchHammers who retired from combat due to lost limbs, psych damage, or just losing their taste for adventure/danger. There's also plenty of people who are hired into the org and provide purely support functions.
Besides the support functions, there's also a more senior WitchHammer leadership that oversees training, planning, and allocating WitchHammers to the frontier. These leaders are all veteran WitchHammers who have claimed at least one Witch Heart.
A team of WitchHammers is usually assigned a ~30 mile stretch of the Frontier to patrol. This will typically have 3-4 villages along the route, as well as a smattering of somewhat larger towns further back from the Frontier.
WitchHammer teams will occasionally band together, either to chase a Witch that is moving across both of their regions, or to try and face a larger threat. In cases like this, if they do manage to claim a WitchHeart, both teams are usually given credit for the kill if they both contributed to the fighting that killed the Witch.
(Note: I thought I would give the players more tools to track down Witches. In D&D5E this turned out not to be necessary, since they already have so many useful abilities)
Calcination - This Ritual reveals an essential aspect of a creature. Fresh blood or bone is best for this ritual, but hair, nails, spit, spore, or other bits can also be made to work. These bits are mixed with certain rare and enchanted powders. The resulting dust is then inhaled, leading to a brief, estatic vision in which one or more aspects of the creature are revealed. WitchHammers usually do this to get a better idea of their quarrie's powers and weaknesses. Better materal components give a signifcant bonus to the Ritual roll. This is useful to the PCs since it lets them identify powers and weaknesses of monsters before facing them directly. A strong success will reveal 1-2 powers/weaknesses of the target.
Sympathy - Forges a mystical link between a part of a creature and the creature itself. Fresh blood or bone is best for creating this link, but hair, nails, spit, spore, or other bits can also be made to work. While this magical connection is usually not strong enough to channel hostile magics through, it can be used to help track the parent creature. The ritual takes 5 minutes & uses up the material ingredient. Depending on the success of the ritual, the resulting charm will last from 3-72 hours, and will indicate the direction and approximate distance to the parent creature. Better material components give a signifcant bonus to the Ritual roll. This is useful to the PCs as an additional method of hunting down Monsters/Witches.
A monster ate my family!
I don't get along with city folk
If you manage to claim the bounty on five Witches, the Emperor will give you a nugget of gold the size of your head. I want that nugget
My one true love was lost in the Forest and I want to find out where she is and get her back
A Monster ate my dog!
I crave the excitement of nearly dying. Every other part of my life is a gray blur compared to the thrill of hunting and being hunted.
I am a hero and I protect people
A monster ate my niece!
My family thinks I am a wastrel and a good-for-nothing, and they sent me to the border to toughen up and prove I am worth taking over the family business
I am a cultist of Ias-sai, and I observe and undermine the WitchHammers from within. Doom is at hand. The Forest will drown the World.
The world belongs to the Empire, and we must burn and drive back the Forest in order to claim our destiny.
A monster infected my dog with corrupting spores, and then my dog ate my niece!
I could learn much by studying Witches and their monsters.
All WitchHammers are given a basic stipend to support them on their patrols. I need that stipend for alcohol
Slaying Witches will make me famous, and will win me the affections of my true Love/many people one of whom might turn out to be my true Love/my family/the Army commander who I hope to impress