WORK IN PROGRESS
Getting there
This boss can found going towards Wintermist follow the trail until you see dead trees. There you can find a NPC by the name of Druid Brewix, interacting will prompt dialogue warning you of the dangers ahead. After going down the vines you find yourself deep below Brightleaf, from here head north and you will face the boss.
Mechanics
WARNING: THIS BOSS CAN ONLY BE FOUGHT WITH ALCHEMY LEVEL 65 OR BETTER. AND CAN ONLY BE FOUGHT USING SECATEURS, THIS BOSS IS IMPERVIOUS TO ALL OTHER FORMS OF DAMAGE
Fighting Back
You might notice, simply walking up to the boss and pressing harvest with your secateurs doesn't work as intended. In order to deal damage to this boss you must first stun them. Use your trusty secateur to harvest the Thorns summoned by Bryomera. After collecting 10 (note that after the elimination of the boss or leaving the area will despawn all thorns/potions in your inventory), head over to the Geyser to craft a Vile Concoction. Throwing this at the boss will stun them briefly, buying you time to harvest the boss dealing damage. At any point if you get stunned by the thorns coming from the ground, you will lose all thorn collection progress alongside any crafted potions. So watch your step!
Drops
>50% Dmg Dealt - 1 drop / 100% - 1-4 drops