Darkwalker
Shortly after Doctor Abracore recruited Hundun, the pair found a reference to a being of "great power and darkness" in some old manuscripts, supposedly locked away under a Buddhist temple in Cambodia. Travelling there, they found the temple had been abandoned years before, in the Khmer Rouge period, and they cautiously sought out the prison beneath.
The mystic wards were all but collapsed, and it took little to no effort to release the being they sought. What they found was a ball of pure darkness, but as they released it it coalesced into the shape of a woman with raven black skin and eyes. She explained that she was the Darkwalker, the guardian of the darknesses in the world, the blighted places and corrupted creatures that stood in the shadows of the earth, eternal enemy of the Lightwalker, locked - until her imprisonment - in eternal battle to maintain the balance between light and darkness.
Darkwalker found the purposes of the Hallows to her liking, and has joined them. She possesses a number of useful abilities, to go into an amorphous, intangible "shadow form", to create constructs of shadow essence, and to teleport from one spot of darkness to another in the blink of an eye. (Doctor Abracore suspects she has greater powers still, but is deliberately holding them back for her own reasons.) One thing disturbs her greatly - while she was locked away for 300 years, Lightwalker appears to have done little, and is conspicuous by it's absence in the world of superheroes and mages alike. She is unsure what to do about this.