Hags are dangerous on their own, They are a predator upon humans, especially lone travellers, but they are not incredibly dangerous to towns or villages. Most of the time, a group of farmers who discover a hag in the area can chase it away, meaning that hags spend their lives in fear, predating on humanity and also fearing them. Hags, however, have a solution to this problem, forming Covens.
Hag Covens are always formed in groups of 3, 9, or 13, though no one fully knows why these are the only numbers. Some say there's a mystical value for these, others believe it's the only way the Covens don't fracture into bickering, factionalization, or even violence. Beyond their size, scholars are not fully sure why these Covens empower Hags. It seems like it should be just strength in numbers, but Hags defy, displaying strange and unexpected powers.
What scholars do know is that Hags are greatly empowered by covens, often able to become a proper danger on the map, rather than a roaming predator. As the Coven grows, they will often begin to build a permanent home. Rather than a hut in a swamp, or an enticing rest stop in the woods, they will build something like a hidden underground complex, a business milling or sewing, or a foreboding tower. The most important caveat is that these are often build in a ramshackle piecemeal way, since the Hags begin these projects scared and expecting to move on, and then adding new pieces as they go along, small addition by small addition, eventually creating a large, ramshackle, home.
As Hags get together in a Coven, they must place something important to themselves into a magical object. This manifests as all of the Hags in the Coven gaining a Trait or losing a Trait. A Coven can, if able, kill a person with a trait in order to have this item gift them that trait, instead of giving up one of their own, when they do this they must still also gain a negative trait when they are not holding the item. If they lose a Trait they must all have the trait to begin with. Many Hags will place their Gift into the object in order to limit themselves, only one of them at a time can do magic. Other Hags will place their sight into an eyeball and all become blind, sharing a single eyeball they need to be able to see. This sharing of a single energy is not as catastrophic as it seems, since when using the object, they gain the powers of all of the Coven. For example, if a Hag is attempting to summon a Daemon using the gnarled staff they all placed their Gift into, every Hag in the group Helps on the Summoning roll, allowing the entire Coven to participate in the test. Though the Coven cannot choose not to help their brethren when their power is being wielded as part of the Coven's core object. Covens who put their sight into an eye might get help on Observation and Perception tests. Others may gain the Lame trait and have a walking crutch that lets them share Speed. The Trait associated with the object should dictate the sharing of power.
The drawback of being in a Hag Coven is that the item associated with the Coven is not only usable by the Coven itself. Stealing the Eye of the Coven might allow a young Hero to see things like an Elf, or a Knight to hold aloft a staff and gain great mystical power (though this has the drawback of the knight not knowing any spells). Hags will do anything to recover their Coven object, especially since the Coven cannot be broken without breaking the object itself. This means that Hag Covens are often a source of powerful magic that comes with powerful enemies to overcome, the start of almost any heroes adventure, though also often the end.
The Sisters of Gethorne are nine Hags living in an abandoned mill in the town of Gethorne where they had settled in under the guise of Wealthy Merchants. As they spent more and more time in the town they would send their sisters on expeditions to trade with nearby towns, buying grain from local farmers to mill and then send members out to sell it at nearby market as flour. This gave them cover to have one or two members slip into the dreams of townsfolk and suck them dry, leading to them dying in their sleep, and the Hags being empowered. As their wealth grew, they began to gorge themselves on the townsfolk's dreams, until finally the town became an abandoned husk, and their mill's heyday but a memory.
Not wanting to move from their home, the Sisters of Gethorne added an observatory town to the top of the mill, allowing them to chart the stars, and use the geometry of the place to build a great Prison Gate in the centre of the old mill floor. There they call forth ghosts and daemons to hunt the roads around the old town for them, or to trade for knowledge and power. They have also constructed a small taxidermy workshop to repair corpses and build small zombies using their practice of death art.
The Coven is based around a set of coins, with the Hags gaining the Unctuous Trait unless they are holding the bag of coins. They are allowed to share their Haggling and Bargaining.
The Witches of the Wyld are a group of three Hags who have managed to seed themselves into a forest, which is called the Wyld Wood. Famously now a woodland where those who enter regularly disappear, though it was once a lush woodland full of dryads and other faeries. The Witches of the Wyld together bear a set of pruning shears which grant the Second Sight, though the members are Blind when not wielding the shears. These shears allow them to share their foraging, farming, and hunting skills.
The Witches have hunted the local fae to near extinction, and traded their remains to the darker spirits of the world. Bringing in the restless dead, and sending them forth, the forest has become deathly haunted, and scattered with the mortal and ghostly remains of those who enter. The Coven has been using their pruning shears to create sacred groves, to give themselves power, and to exalt their cthonic deity. They have created several grizzly scenes as chapels where they worship their deity, and bring in heretic priests to engage in bloody worship. The Coven has fully reshaped the forest into a blight upon the map.
A Burning Wheel Monster Every Week