Standing inside the Forest, you see ancient but healthy pine trees, stretching 60-80 feet into the air. These trees go on and on, as far as the eye can see, each one bearing a family resemblance to each other one. Regardless of the season, the air is slightly warm during the day and moderately cool at night. This effect begins once you are even a few feet inside the Forest. The trees block out most of the sun, and a faint mist hangs in the air, so that even at noon the light seems soft and twilit. At night, the moon and stars are generally hidden, though a faint ambient moon light illuminates things regardless of the phase of the moon. On random nights and locations, even this goes away, and the Forest becomes an absolute pitch black. There is only slight underbrush in the Forest, but the ground is uneven, rocky, and laced with roots to the point where carts are basically useless and horses are at a constant danger of injury. Only really surefooted animals like donkey's are of any use in the Forest, though they and all normal animals are going to be skittish and prone to panic in there. There is a constant, soft smell of leaves and decaying leaves. Sounds are slightly dampened, and it can be difficult to pin down which location they are coming from.
The Forest is a gigantic and subtle aberrant creature, so large that it is halfway to being its own plane of existence. Every part of the Forest is functionally identical to every other part of the Forest. Once you've gone about 100 yards into the Forest, things will appear basically the same as when you've walked 1000 miles into the Forest (though you will be in greater danger the further in you go). In small and gradual ways the Forest will try to make itself unnavigable, and will lure and misdirect people deeper into its depths. Trees, leaves, undergrowth, even the dirt is subtly and maliciously adjusting itself over time. A glade or a creek that is there one day might have disappeared a week later. Damage or burnt sections will repair themselves in a day or two, leaving no trace of previous actions. Fresh "100 year old" pine trees will cover over battlefields, corpses and armor will sink beneath the ground. An expert ranger has a chance of navigating the Forest, but it is very difficult for untrained people to make a journey of any length through the Forest without some sort of magical assistance. Compasses do not work inside the Forest or give misleading results, maps are of course useless, and even the stars will twist and reshape themselves when viewed from deep within the Forest. If PCs try to make marks to leave themselves a trail, the marks will either disappear or be subtly altered if they are out of sight for more than an hour.
If players use spells that sense magic/aberrants/evil, the Forest will register as a giant, blazing beacon of hostile magic that is all around them. By the same token, tracking things in the Forest using magic is difficult, since the Forest has an extremely high level of background magic that drowns out most other sources of magic. So in the Forest it's difficult to track things that are far away, or that that have a weak magical signature.
While in Civilization, things are generally OK. You can find food, water, inns, garrisons, people to trade with, roads and maps, supportive peasants, etc. etc. There are occasional mundane threats, as well as incursions from Witches, but for the most part in this phase of a scenario the PCs are in less danger. The Forest is the opposite of that. Getting fresh supplies is difficult, navigation is very difficult, there is no help available, and there is no upper limit on the threats one can meet in there. Or to put it another way, the Forest is where PCs die. The PCs should learn to kind of hate the Forest. If they venture into the Forest, they should want to finish their business there and get out again as quickly as possible.
Within the Empire, as you travel from the frontier and towards the capital, you run into more people, larger cities, more resources, more guards. You go from outpost garrisons of a dozen men to armies of thousands. In the same way (though not as immediately visible), the deeper PCs travel into the Forest the greater the threats they will face. At the borders of the Forest threats will be at least potentially manageable. If you travel three hundred miles into the Forest there are monsters the size of hills, and living glints of light that can tear a mind apart, and a hundred deaths that do not even have names.
The Forest is in many ways its own realm of existence, and it can occasionally lead to other planes of existence that are even further away from baseline reality. PCs that try to travel on moonless nights are especially vulnerable to this sort of inadvertent plane-shifting. Feel free to decide where they end up; a destroyed and drained realm of shattered earth and hungry shadows, a timeless plain of flowers and eternal sunshine where old horrors are buried beneath the ground never to trouble the multiverse again , a realm of cubes and lines and endless flowing waters, etc. etc.
The basic idea is to take one one aspect or experience in a character's life, and then blow that aspect up out of all proportion until it eclipses every other aspect of their life. Whereas normally people give at least some consideration to other people's desires and needs, Witches do not value those at all, and instead are wholly focused on their own overriding desire/trauma. E.g. the character likes money? Ok the Witch version of them only cares about money, and will happily lie/steal/murder 100's of people in order to take their shinies, and will keep doing this for centuries unless they are stopped. The Witch might still have a gloss of their old personality over this new nature, but it is only ever a gloss and will not constrain their behavior in any meaningful way. So, in summary, they are entirely self centered and dedicated to their own passion above anything else. In terms of powers, I usually follow the same method, and take one aspect from the Witch's original life, and then base all of their powers/monsters around that aspect.
Side note: I was reading Wuthering Heights recently, and it provides a decent approximation of this witchification process. E.g. you have a Heathcliff character, he has one bad experience, and then he decides to make that bad experience everyone else's problem for the next 20+ years. Whereas most people would change, forget, forgive, become distract, etc. nope! To him it will always and forever only be about that one singular passion.
Central to the idea of Witches is the idea of infection and corruption. Give them powers to infect, posses, mutate, or otherwise convert their targets. Witches and their monsters should be cancerous, robust, and difficult to completely kill. Give them multiple forms and stages, i.e. as a general goal you want them to have 3 phases or forms that need to be defeated to completely kill a Witch. Try to give them a back-up form too, one last ditch ploy to preserve a part of their power/essence even if the rest of them is destroyed.
A Witch is created when a person swallows or otherwise absorbs a witch-heart. A witch-heart is a small, gray, somewhat jagged stone. The stone has an odd, shark-skin like texture, that snags and abrades the skin if you run your hand across it. The stone is slightly warm, and it is necessary for a Witch to live. Most of the time removing the witch-heart is immediately fatal to the Witch, though sometimes they will continue to live for a few more minutes. In extremely rare cases a Witch has survived this process, but afterwards they have only a shadow of their former power. In order to claim a bounty, a team of WitchHammers will typically turn in the witch-heart of the Witch they have killed. It is rare to be able to claim a bounty without the witch-heart, since Witches are so mutable and so survivable that it's difficult to truly know that you've killed one without the heart. There is no known way to actually destroy or damage a witch-heart.
Witches get witch-hearts by venturing out into the Forest alone. What happens from there is known only to the Forest and to Witches, and they are not talking, or if they are talking they are lying.
Witches are solitary creatures, since their nature makes them unable to effectively interact with most creatures. For their few interactions and trades, they use witch-gold as a medium of exchange. These are small gold coins with an indistinct profile and symbols on their time-worn faces. The coins are slightly warm to the touch, which is because they are subtly alive and intelligent. If unobserved, the coins are capable of extruding small golden spider legs and scuttling away. Given darkness and time, they can even hatch into young monsters, which will in turn scuttle off to try and grow into full size beasts. These coins bring bad luck to their owners, but unlike witch-hearts they can be destroyed. The coins burn surprisingly well and with a cheerful blaze.
Yes! Witches are vicious baddies, no redeeming qualities. They will happily lie and dissemble and put on a facade, but in the end they are wholly monstrous. You can occasionally make a temporary deal with some of the saner Witches, but that's about all you can say for them.
The stat blocks for Monsters list their Health, Defense, Strength, and Agility. Most of these should be fairly self explanatory. Defense is the most ambiguous one; it is a general measurement of how hard it is to stab the creature with a sword or shoot it with an arrow, and it combines the creature's armor, skill, experience, and innate magics.
These ratings aren't meant to be absolute values, rather they are more impressionistic to give a general idea of how the creature can perform in combat and what its role is. E.g. a creature with a Health of 10 should be a big old kaiju of a meat shield, requiring large amounts of damage over multiple turns in order to destroy. A creature with a Defense of 5 should be an opponent of about the hero's skill level, while one with a Defense of 11 should be fiendishly difficult to wound, and perhaps require cornering or attacks from multiple angles. A creature with an Agility of 1 is lumbering and clumsy, while a creature with an Agility of 8 can easily do backflips and handstands. Etc.
As a baseline, a normal human soldier might have a "3" rating in all of these attributes, while a standard PC might have a 4 or 5 in these attributes.
One thing to consider with these stats is that Monsters and Witches often have stats that are out of proportion to their size and appearance. E.g. a Witch might seem like an underfed teenager, but have the strength of a lion and be able to tear a shield in two with their hands. Similarly, these unnatural creatures rarely feel pain, and can often take wounds that would kill a natural creature many times over. Witches in particular have to hacked apart, and even then they might not be dead, just disabled and twitching.
The business of translating these stats to the exact numbers of your game system is an exercise that is left to the reader. They should be adjusted based on the game system, the level of the party, the skill of the players, the player's appetite for challenge, etc.
As written these adventures are system-agnostic. Our group used D&D5E, but that was mostly because all of the players were very familiar with D&D5E rather than because the system was a perfect fit for the adventures. Ideally, you would play these adventures with a system that has moderately less powerful PCs, since that way its easier to challenge them and to have the horror elements of the setting shine through. It's difficult to make even a medium level D&D PC really afraid, which is ideally what they should be feeling when inside the Forest. I did have some house rules to constrain D&D at least a little bit; there is no teleportation in the system (as that would completely break the dangers of venturing into the Forest), healing items are very limited, magic items are somewhat limited, and resurrection is basically non-existent.
In many cases, it makes sense to have a large amount of time between adventures. The Frontier is dangerous, but it is not so dangerous that a new Monster is threatening the PCs every single week. There's usually about 6-24 months between threats. Give the PCs a chance to talk about what they are doing during this time, where their mind is at, what skills are they honing, how their relations with each other and the towns people are doing. Also use this time to indicate how the Frontier is changing, e.g. the growth of a village with an influx of emigres, the backstory/character/culture of the new arrivals, or the founding of a new village on the ruins of an old one.
In some cases it makes sense that adventures are closer together in time; e.g. the PCs act against the Forest, the Forest retaliates in a few days or weeks.
Since these adventures are fairly self contained, the larger structure/metaphysics of the world is usually secondary/irrelevant. But! If you care, at least in my game, the world is home to two Godlings. The Godling Sai-ias is ~Apollonian (e.g. order, logic, rationality) and founded the Empire to act as its vehicle/agent/tool/champion. The other Godling, Ias-sai, is ~Dionysian (e.g. emotion, intuition, wildness) and created the Forest to act as its champion. The world is a testing/training ground for these two creatures. When one Godling has entirely remade the world in its image, it will have shown it is ready and will be promoted to the next plane of existence. The loser Godling will be held back a grade and forced to try again, and the world itself will be recycled at that point. The Witchhearts that the PCs gather are tiny, tiny shards of the Dionysian godling that it has given to create Witches, while the relics carried by the priests of Sia-Ias are in fact small blobs of their god that have been broken off from the main body their God and sent out into the land to be used to perform miracles.
Anyway! That was my metaphysical backdrop, feel free to use it or create your own.
a greedy, sneering merchant from one of the merchant houses, who will try to take advantage of your situation or need
a friendly, naive, farm hand with a wagon
a gruff farmer who doesn't want nobody in his business
a wandering minstrel, who is down on his luck since he is terrible at singing and minstreling
a gang of very tough young kids
an extremely drunk old man
a mayor (Samantha) desirous of the safety of their town
a rich scholar (Chris Pound) who is writing a travel guide to the borderlands
a laconic goat herd
A young monk who has taken a vow of silence
an ebullient and strong farm hand (Roberta)
an annoying kid. "wat ya doing? why?"
a testy noble, visiting an ill-advised country estate (Vincent)
a friendly and fundamentally ok trader (Ravi). "my friend"
an old lady who will want to talk about herself
an old hermit who misunderstands everything you say
a card sharp who will pretend to be friendly and lie and to try find advantage
an clam breeder, who will try to sell you fried clams. suggestitive
fletcher, who will try to sell you arrows. suggestive
a spear maker, who will try to sell you spears. suggestive
NPCs you will meet along the way (2)
a ant-plant orchard keeper. only eats plants
a wine maker that runs a failing vinery. very drunk. very friendly
a group of head-in-the-clouds monks who are studying clam genetics
a group of orphans who will try to beg money. and keep coming back for me. Talk in baby voices, have pet dogs
a weirdo who keeps a pig farm on the edge of town. unfriendly
a merchant caravan, friendly and will let you know the news and help as they can
a messenger on a lathered horse, no time to talk, rushes by
an army contingent of 20 men. no-nonse martinent commander
a shady group of ruffians. neo-priests of Davkul
a man having sex with a sheep (at night)
a man who's been hanged from his foot. he sold somebody a bad pig. otherwise friendly
a man in stocks. he is severely unpleasant and insulting
a man with 2 tame pigs (Shana and Sarah). he oinks sometimes instead of talking. 14)
One of the goals of this system is to make the GM's life easy by making it easy for them to generate and run adventures. To this end the adventures are episodic, mostly self contained, and meant to be completed in 1-3 play sessions. I'm really bad at remembering things for more than a few weeks at a time, so this structure lets me avoid having to remember long-term plots and such and instead just create and run smallish weekly adventures.
The lack of a long-running plot also means that players can drop in and out of the game without disrupting the story too much. So these adventures don't really progress into defeating some grand plan or big bad, and instead are just (hopefully) bite-sized, fun, weekly things.
There are three main elements that go into a Forest:
A fae or fairy of fairytale realm, that operates on its own sort of dream logic, and can be both wonderous and cruel.
a sort of Puritan fear of the dark and primeval domain where the laws and meanings of civilization fall away, and reality takes on a baser, more barbaric, more terrifying aspect.
An Annihilation type Zone X, a subtly mutated and changed land that only appears natural, but is actually infectious, cancerous, corrupting.
For my adventures I went with about 20% Fae, 30% Puritan, and 50% Annihilation. Obviously you could change this for your own Forest. You could lean into more the Fae aspect and make it something more like the standard D&D5E Faewild adventures, with more humor and wonder, and where there's more opportunities for diplomacy or peaceful interactions or simply experiencing the strange and alien. Or you could have a more Witcher type campaign, with the PCs as mediators between civilization and Forest, and trying to decide what the just/best solution is to the conflicts that arise between them.
For my game I was really only interested in the conflict along the Frontier between the WitchHammers and the Forest, so I didn't put much effort into developing the world beyond that . Also I'm lazy. So I made the Empire as simple as possible, where things are generally rational & reliable & clearly worth fighting for, and there are no dark plots going on underneath the surface. But, if you wanted, you could add in more elements where the PCs interact with civilization. E.g. threats from bandits, or injustice and revolution, or corrupt mayors or merchants that have to be dealt with, or competing power blocs inside the nation, etc. etc. Basically the full list of normal plots.
The Black Spot (on Netflix) has perrrrrrfect imagery of what the Forest should look like.
The Witch, Annihilation
Countless monster hunter shows, e.g. X Files, Grim, Buffy, Supernatural, The Witcher, etc.