Surface research of the ebon-whorled stake has you skimming along quite a
few paths, though the clear common theme is that they are tools used for
the hunting of nethrim. Many stories claim that a wooden stake - most
noting it must be made of oak specifically - can be prepared with the
proper rituals to not only slay a nethrim, but draw out the nether-taint
from the creature. The intended purpose of this particular nethrim-slaying
method is that the tainted soul is then unable to escape and find a new
vessel to inhabit, or at least diminished with each slaying to that end.
The preparation rituals vary from tale to tale, but usually involve an
Immortal - most commonly Aphraen and Serafina, though Iarel and Bogvaskr do
occasionally get mentioned, and there's even one invoking the Mountain
Father of the Giganti.
Perhaps the most prominent legend involving using oak stakes to hunt
nethrim is that of Ylvarra, a Faewyr huntress. When several villagers were
found dead with terrible bite and claw wounds, Ylvarra took it upon herself
to look into the matter. She followed the tracks for several days,
receiving notes carried by falcon each morning telling that more villagers
were going missing. On the thirteenth morning of her quest, deep in
unfamiliar woodland, she received a note informing her that the culprit had
been discovered to be a local rabid bear that had been put down, and the
note went on to call her back home.
Not wishing to return home empty-handed, the huntress resolved to follow
the beast she had been tracking for one more day, which led her to discover
the den of the (you note the text specifically calls it 'the', not 'a')
Werewolf. After a fierce battle during which her bow was snapped, Ylvarra
managed to slay the beast, but noted 'as her dagger snapped off just above
the hilt with the killing stroke, a foul black wind burst from the beast's
corpse to flee the cavern'.
After a long trip home, greatly delayed by the need to tend her many wounds
which 'seeped and refused to heal well', Ylvarra found the villagers to be
somber and mournful, but glad at her return. However, her rest that night
was interrupted by an unsuccessful ambush by 'former friends who had become
long-limbed and bestial at the rising of the moon, raking with claws and
biting with fangs'. The unarmed huntress fled to seek cover in the woods.
Dismayed at what had become of her people, Ylvarra resolved to put an end
to their now twisted and maddened state. She knelt and offered a plea to
Aphraen to aid her in returning peace to the night, and upon opening her
eyes she found herself looking at 'a stout limb of oak, lying in a moonbeam
at the base of a great and ancient tree'. After sharpening the end of the
wood with a stone, she made her way back to her village with this weapon
given her by the Guardian of the Night to slay the monsters that her fellow
villagers had become. As she faced the last of the feral man-beasts, she
'Gazed upon the visage of her once-friend, only to see the golden eyes of
the same Werewolf staring back.'
Empowered by Aphraen, Ylvarra managed to once again defeat the Werewolf,
dealing the killing blow by plunging the stake into the monster's heart.
Only this time, 'as small wisps of a foul miasma began to to rise from the
corpse, tendrils of black began seeping into the oak-stake to whorl it with
veins of darkness that were the evil beast's very essence', and the
Werewolf was then slain in truth.
Adding to her tragedy, Ylvarra found herself showing signs of being
afflicted by the same curse her fellow villagers had - her nails and teeth
began to sharpen, her limbs to lengthen, and her hair to become 'thick and
long like that of a beast'. After burning down her village, Ylvarra fled
into the night to a solitary life of self-imposed exile, though she often
features in other monster-hunting tales, always intending to deal the final
blow with a sharpened stake of oak blessed by Aphraen in order to contain
the evil soul and prevent it from finding a new vessel to inhabit.