The Briarwild is a massive thorny cancer that forms on the crossing points to the Aelfpaths, Feywild or as a result of blighting a normal Briarwood .
The initial presence is a ball of massive thorns and rotten berry vines that takes over the outer Briarwood wall or is a ball, growing from the center out. It grows 5′ per hour until it encompasses the Briarwood, or grows 150′ diameter by 50′ tall. At its center is a small, frost covered chamber about a 10′ sphere.
Eventually, the inner sphere freezes completely. From it will issue massive walls and clouds of fog, winds of cold frost, pestilent winds of sand, and all manner of howling and terrifying sounds.
The ice ‘egg’ gives birth to a pulsing ring that is a step-gate, connecting to any nearby Aelfpath, and to the planes of the wyld and shadow.
Most Briarwild’s end at phase 3. Only if a Faegrimm finds its way to one, it can make a DC 10 Sanity check to try and bond with it, the Briarwild connects with the Faegrimm, wrapping it in a sado-masochistic thorny crush. The tormented Faegrimm‘s blood pours across the thorns in ritualistic embrace wherein the tormented soul of the Faegrimm and Briarwild become one. The Veil of Madness has a palpable miasma of antipathy towards elven characters.
Travel through the dense briar patch: Each 5′ will cause d4/2 piercing damage and 2 poison damage (DC 10 Constitution for half); this is considered magical damage. Hacking through it causes the path to be sealed behind the character(s) as they go. For each 5′ of hacked movement, it takes 1 round and regrows in a single round; Each 50′ total of movement requires a DC 10 Constitution check or the character gains 1 level of Exhaustion. Burning can be done at 10′ per round, and it takes a full minute to grow back. However, if the briars are burned, it releases a nasty toxin of d8/4 poison AND d6/3 acid; DC 15 Constitution check for half.
Eye of the Wyld: The center chamber has a green-black glow and frost forms over anything that enters it. For each round, the character will take 2 cold damage (DC 5 Constitution save for half). While inside the briars, anyone speaking Feyloise, Primordial, or Sylvan causes its hearers to make a DC 10 Sanity check or take D6/3 psychic damage. This is for spoken only.
Circle of Transport: The energies of the Feywild, Shadowfell, nightmares and dreams, and any local Aelfpaths all become accessible. Any character with Misty Step/Fey Step can get through without damage, otherwise the ring will do d10/5 necrotic damage (DC 12 Constitution save for no damage).
All elven characters recieve a -2 penalty to any saving throws inside the Briarwild. The presence of an Elf within the group will trigger the Veil of Discord for those passing through the Briarwild if it has become a Veil of Madness: