Shadumbra is a nightsaber that used to roam the forests of Ashenvale. She has now taken to wandering very close to Raynewood Retreat since the Cataclysm.
Killing her used to be one of the objectives of The Ashenvale Hunt. Defeating her will still allow looting of her head, which can be turned in to Senani Thunderheart at Silverwind Refuge.
Like Ursangous, she cannot be tamed by hunters.
Note: These quests are no longer associated with this particular mob/NPC/item.