"Racism is man's gravest threat to man - the maximum of hatred for a minimum of reason."
- – Abraham Joshua Heschel
"The trees have grown wild and dangerous. Anger festers in their hearts. Black are their thoughts. Strong is their hate. They will harm you if they can."
- – Treebeard
Drycha (AKA the Briarmaven of Woe, The bitch who will cover your army in bees and The Angry Tree) is an ancient and powerful nature spirit and probably the most racist individual in Warhammer fantasy or Age of Sigmar. Considering this is a setting that includes the Skaven and the Dark Elves, that's saying something.
Fans tend to describe Drycha as crazy, evil, and hot at least part of the time. She is also, unlike other dryads, depicted as anatomically correct by human standards (having at least a navel), much to the /d/elight of certain fans. This continues with the new model, as Drycha's humanoid part looks clearly feminine, though between the legs of her tree body are some ...unfortunately placed vines.
Her earliest lore established that Drycha was old even by dryad standards, predating the Elves leaving Ulthuan, and may have been one of the first dryads in existence in Warhammer. Originally Drycha held court amongst the roots of Addaivoch, the once-glorious creature known in later times as the Tree of Woe, which got that way after Morghur was killed there. While some believe that Drycha lost her mind when Morghur’s death tainted the ground of her glade, she was insular, capricious and malevolent for many long years before that.
She first came to prominence after the Wood Elves entered an alliance with Athel Loren. Drycha did not like it. AT ALL. In the early years of the alliance between the Elves and forest, Drycha was ever in evidence about the glades and groves, watching the Elves and examining their every action for any sign of betrayal. She rarely conversed with others, even the Dryads who served her as handmaidens, but instead chanted a mantra of the names of all those fellow spirits whom she believes have been failed by the Elves. It's unlikely her list would ever end because, despite her age, Drycha's memory was crystal-clear and new names were added with every battle between Athel Loren and the outside world (Dwarven-level grudge there). She was in regular contact with Coeddil, a racist old Treelord Ancient who was held in high regard by Drycha (like a how a member of /pol/ would view a Nazi; Coeddil was like Grandpa Dreadnought but racist and more susceptible to corruption). Coeddil had attempted a coup before by trying to stop Orion's rebirth, but he was thwarted and imprisoned by Ariel.
As time went on, Drycha’s activities became more violent and worrying to the Wood Elves. On the fringe of the great Drakwald Forest in the Empire, peasants told stories of the trees that come alive, hungry for blood. On the edge of the Forest of Arden in Bretonnia, villagers gather only deadwood for their purposes, citing tales of other settlements found ruined and torn, the inhabitants left as scraps of tattered meat by the vengeance of the trees. To many, these events seem as senseless as they are apparently random, but if they are indeed the work of Drycha and her handmaidens, there must surely be a greater goal behind them than mere slaughter — though what that goal is remained to be seen. Popular consensus was that she was trying to break the alliance between the Bretonnians and the Wood Elves. Drycha did stage a coup during one of Orion's absences only to be thwarted by a Grail Knight. Drycha disappeared after that, her last act beforehand being to help break Coeddil out of the prison Ariel had bound him in.
In the End Times, things really went sideways. Drycha went to ground with Coeddil, her head full of schemes of vengeance against the Wood Elves. To that end, she committed her first act of open treachery captured the Fey Enchantress and gave her to Mannfred von Carstein to bring back Nagash (which is like using a nuke to stop a squatter from trashing your house). Then she just sat on her hands for awhile until the final battle for Ulthuan, where the remaining High and Dark Elves were evacuated to Athel Loren. While there was no direct word about Drycha, the forest spirits were largely unhappy about this turn of events and you can bet that Drycha would've been at the head of any tree-klansman meeting. Drycha's hatred was so fierce that she was easy prey for the demon prince Bea'lakor. After swaying the cultists of Khaine, disillusioned about Malekith outlawing Khaine's religion in the wake of all that trouble the Widowmaker and Tyrion had caused, Bea'lakor played on the forest spirits' hatred of outsiders. Coeddil was revealed to have been tainted by Chaos and embraced Bea'lakor's plan, with Drycha following Coeddil's lead; had Drycha known the truth about Coeddil and Bea'lakor she would've had nothing to do with them, but she couldn't see past her hatred.
So a host of Khainite elves and forest spirits attacked the army around the Oak of Ages; if you're wondering why Drycha fought alongside the Khanite elves despite her hatred of non forest-spirits and wasn't suspicious of them like she was before, your guess is as good as mine. At one point she got into a duel with Malekith, and did surprisingly well. While nearly everyone was distracted Bea'lakor went for the Oak of Ages. As the daemon prince sunk his claws into the wood the earth shook, sending everyone sprawling as the magical weave the tree maintained was corrupted. Drycha looked to the Oak of Ages and saw Bea'lakor. In that instant, she realized the horrible truth of how she had been used. She had been manipulated by the daemon to give it a chance, and now it was going to try and destroy the world. Drycha immediately turned to stop the daemon prince, but was decapitated by Malekith, who knew that Drycha had been manipulated but deemed her too erratic and violent to trust.
Age of Sigmar
During either the End Times or the Age of Myth Alarielle had somehow recovered Drycha's soul in something called a soulpod. While Alarielle made the Sylvaneth she refused to plant Drycha's soulpod. This was because Alarielle feared the damage that Drycha’s firebrand madness might do and the horrors she might wreak. The Everqueen worried also that Drycha’s was a necessary darkness, and that by keeping her imprisoned, the mother had somehow weakened her children.
At her lowest point during the Age of Chaos, Alarielle planted her barbed seed in the hateful chasm known as the Hamadrithil, desperate for someone to take the fight to Chaos. An ancient and malicious sentience dwelled in Hamadrithil that Alarielle hoped would make Drycha strong. The Everqueen got her wish and more. When she burst free from the rift, Drycha was no longer a mere Branchwraith. She was Drycha Hamadreth, a being encased in a body of twisted vines and gnarled thorn-root, the embodiment of the Hamadrithil’s malice given form. Her memory and sanity were fractured and she was torn between rage and depression, but Drycha was otherwise the same as she was before. Drycha’s bitter soul drew deadly spites to infest her form, flitterfuries that came to bask in the heat of Drycha’s rage while the squirmlings suckled at her sorrow.
She drew the Outcasts to her in great number, along with other disaffected clans besides. Drycha’s first host was uncontrollable, a force of nature’s wrath that ripped through the allies of the sylvaneth as readily as their enemies. Unable to fully command her wayward daughter, but unwilling to destroy her, Alarielle was forced to name Drycha an Outcast herself. This seems only to have strengthened Drycha’s resolve, for she rules the other Outcasts as a twisted queen in the place of their estranged mother. Drycha sings her own song, a discordant dirge of hatred for all those not of the sylvaneth. Drycha has no mercy for her foes since, in addition to using fear as a weapon, she's not above toying with her foes before she kills them (read; torturing them and drawing out their deaths).
Now Drycha seeks only the total dominion of the sylvaneth over the Mortal Realms and the death of everyone else. She will fight however and wherever she feels she must until that end is achieved; with other wargroves, by herself or even at the side of those flesh-and-blood beings she hates, providing that to do so furthers her genocidal aims. That's right, a racist, insane, genocidal terrorist is a "hero" among the forces of Order. Drycha herself remains an agent of anarchy and destruction with a hatred of non-Sylvaneth, though she retains a grudging loyalty to her mother goddess and a love for her people that keeps her on the side of Order.
On the Tabletop
In Warhammer Fantasy, Drycha was weird. Her first incarnation was mediocre, and there was a big drawback for both; an army containing her could only have units with the Forest Spirit rule. She was rather expensive for a Hero, at 255 points, but she didn't come with nearly enough stuff to justify this. For starters, she was a Level 2 caster and only had access to one lore. While she's reasonably fighty (she gets +2 attacks per lost wound, no life shenanigans), she was easy to drop. While her kinda ganky Deep Strike ability seemed fun, you're only guaranteed d3+1 Woods max (IE the one you brought, sitting in your half of the table, and the acorn of eternity if you brought it) it was probably easier to just have them join her from the front and thus Drycha was usually deemed not worth it.
Age of Sigmar was very kind to Drycha crunch-wise. She is a durable and heavy hitting named unit. Capable of leaping across the board with an insanely speedy 9" move, one which isn't altered by any damaged state no less. She also has some magic that gels well with Spite-Revenants. At close range is the best place to use Drycha, where she has a wound and damage output from shooting and melee combined which can rival that of Alarielle and surpass a Saurus Oldblood on Carnosaur. She can also switch between profiles reflecting her new bi-polar nature, with her angry profile making her hit harder in melee while her sad profile can mitigate negative effects she suffers on the damage table. While not perfect, just pairing her up with a couple of basic supporting units will offset most of her shortcomings, and she seems to have almost been tailor made to work with the Spite-Revenants. In fact, she's so good at that she has a unique spell which ties into them, allowing her to use their Bravery lowering abilities to charge her own powers, then in turn offering them re-rolls to Wound. Overall Drycha is worth her points and can be a major threat to either armies of MSU or hordes (but not both at the same time).