The Briarwild is a manifestation of the void’s Twisting of a Feywild Crossing. Most commonly, the cause is a corrupt elven soul who has become a Feygrimm and sit at the crossing point seething in hatred for the sunlight they shall never know. Sometimes a Briarwild forms when foul magics are performed at a crossing – evil, malicious necromantic and death magics which are so intense that it forms a Twisting using a life energies that are consumed in the fell magics.
Feygrim is an elven denizen that was once a dweller on a material plane continuum. However, they have aggressively and extensively entered and used the Feywild to their own selfish ends to claim power, harming its denizens in the process without care. At some point they use evil necromantic or powers of death upon the native denizens and open their heart and soul to The Void, turning themselves into a Twisting. They feel alienated and psychosis takes hold. They pine for their days in the sun, but can only watch helplessly as the sun rises on the other side of a Fey Crossing. Soon they settle on that Fey Crossing, and guard it from those who would come from or go to the sunlight beyond. The crossing becomes a place of danger, and is warped around the Feygrimm – it becomes as a lair to a dragon – a place where few dare to venture for fear of the power the Feygrimm wields in its home. The crossing becomes unusable.
Over repeated sojourns, the time cycles of the Feywild have forever altered their metabolism and chemistry. Their hair is white, their lips thin and skin becomes pale – they are sensitive to sunlight and can no longer dwell on the material lands of their home, but they are repulsed by the denizens of the Feywild and so have no homeland any more, no roots, no connection to other living things. When the Feygrimm has roosted in their Fey Crossing lair for a cycle of 30 days (as reflected outside the land it connects to outside the Feywild), the Feygrimm becomes a corrupt and faded spirit… it loses all ability to speak and can only spread fear and terror (DC 8 + proficiency bonus + CHA adjustment).
If during this time the Feygrimm somehow succeeds in killing a sentient being at the Fey Crossing, the Fey Wild responds. The Feygrimm makes a DC 20 SAN check; if they fail nothing happens – in another 30 days the spirit will fade into oblivion. If they succeed, a material form will be generated for the spirit – a Homunculus. this body will grow first, then a Briarwild will grow from it. Once the Briarwild is grown, the Homunculus can roam free inside of it, without any of its powers affecting it; In fact the broken form controls the nightmares it brings forth.
If the homunculus is killed, a Death check failure means it it remains in this form – otherwise it reverts to a deformed version of their previous physical self (all things tarnished – including his soul); DC 10 Religion check to know the ritual to purify; or Use Divine Channeling to automatically remove the curse. The intact Twisting of the broken form leaves it imbued with extremely potent magics – though thoroughly dangerous.