Necromancer (Terror by Torchlight)

In the aftermath of the Fourth War, a human necromancer or sorceress of unknown identity attempted to overwhelm Duskwood with an undead army by corrupting the Torch of Holy Flame. She was described by Flynn Fairwind as a human or former human dressed in a hooded gray robe with tangled black hair. Her eyes glowed green and her face was sunken and discolored as if she were dead, but Flynn somehow didn't think she was. Her voice was hollow and wherever she tread, the grass rotted under her feet.

After the necromancer stole the Torch of Holy Flame from Forlorn Rowe, Sarah Ladimore—the commander of the Night Watch—tried to search for the missing artifact but was struck with a rotting disease. Upon arriving in Duskwood and learning of the threat posed by the undead, Flynn Fairwind and Mathias Shaw pursued the necromancer into the deepest level of the Dawning Wood Catacombs, where they found her attempting to corrupt the torch with dark magic. She noticed the rogues' presence, prompting Shaw to reveal himself and ask about her purpose while Flynn remained hidden and used his rum to wash away the bone powder making up her ritual circle. The necromancer claimed that she had no interest in Morbent Fel, the area's former resident, and that her vision was much grander than his: she had seen visions of the Jailer's upcoming attack on Azeroth and intended to prepare for Death's arrival. She referred to Duskwood as one of her "old haunts" and claimed that her goal was to eventually move on to attacking Stormwind City itself. After Flynn finished destroying the circle, Mathias attacked the necromancer and managed to wound her throat while Flynn grabbed the torch. The necromancer cursed Mathias with the same disease she had inflicted on Ladimore, but the two rogues managed to escape the catacomb and headed for the Twilight Grove on gryphonback in order to remove the torch's corruption by bathing it in a moonwell. The necromancer pursued them on her mount—a grotesque, winged undead horse—and blasted them off their gryphon as it came down to land in the grove.

While Flynn took the torch to the moonwell, the necromancer began fighting Shaw. She demoralized her foe by revealing that dark wings would come to take away what the spymaster held most dear. Moments later, however, Flynn plunged the torch into the moonwell, reigniting it and allowing him to set the necromancer's cloak aflame. As the fire consumed her flesh, Shaw plunged his daggers into her throat, killing her.

With her death, the unnatural illness afflicting Shaw and Ladimore vanished, and the Night Watch subsequently recovered the Torch of Holy Flame to once again keep Duskwood's undead at bay.

Quotes

 * "I've seen things changing, Spymaster. Visions in the rot. Decomposition making truth plain. Those close to life and unlife can feel it in our marrow. Death comes for the soul of this world, and I intend to prepare for its arrival. I've my sights on finer cities than Duskwood, but it's always fun to visit one's old haunts. So many dead things to play with. Maybe I'll take the king's spymaster with me when I head to Stormwind. I'll turn you against everything—and everyone—you love. You're no stranger to killing, are you, Spymaster Shaw? You'll adapt easily."
 * "Dark wings take away all that you hold most dear. And what a day that will—" (to Shaw, before being cut off by Flynn)

Speculation
Theories as to her identity include:
 * Althea Ebonlocke, given she was killed last time we saw her as she had joined the Veiled Hand due to corruption of the Night Watch by Detheroc. Her father Mayor Ello Ebonlocke had also joined the Veiled Hand. There's also speculation that both the murdered Ebonlocke in Karazahn is her family member or ancestor, as well as the warlock, former First of the Black Harvest, and former demon Kanrethad Ebonlocke also being a family member. Thus her family tends to the evil.
 * Eliza, the undead wife of the alchemist Abercrombie.

In both cases the character would've had sufficient knowledge of the region to know where the Torch would have been, as well as general geography and where to go.