No one knows anything about the past of this Witcher. In the darkness, he cannot be seen at all, but in the light, the shadows are the only places one might expect to find Umbra.
As child, Umbra was always in the shadows. His was a birth by mistake, and though he parents fed and clothed him, they never once loved him. He never knew what it was like to be loved and he never learned what it meant to love. When he was old enough to walk and eat from his plate, his parents walked out without a word, leaving behind no clue to where they went or if they will be back. He was not able to make any friends and he spent his life all alone. Umbra died before he reached adult maturity because his health was insufficient to last him longer. He died with tears in his heart, but none on his eyes – nobody taught him how to cry.
Revived and stalking the world, Umbra was nothing yet he was everything. In the shape of a human, Umbra is seen as nothing but a shadow. When in the presence of his target, he extracts the memories of the target and those around him before deciding who he will become. From the behind the corner of the alley, he would reshape and take on the form of his victim’s late wife. He approaches with the exact gait she has, moves her hands hesitantly exactly the way she does and speaks with the same voice she has. His victim gives in to delirium and lets his guard down. He then begins his feasting, devouring his victim while still alive, but preferably unconscious.
He may be a hungry Witcher, but he is unwilling to give away his presence, preferring to stay in the shadows of the world and continue feasting all he wants. He is not frightened of being found out. He is bored with how weak the world is compared to his powers and would rather forgo the tedious need to slay his enemies one city as a time.
In the worst scenario where the guards are alerted and a party is sent after him, he releases the memories of the woman he held and takes on the form of a great titan, towering above the city, destroying sections of it just with his leg taking on the form of the titan’s leg. With speed, Umbra smashes the city and crushes it underfoot, leaving beneath a flatten mess. After feasting upon the remains of what he needs, he buries the entire city, leaving behind an empty plain. Travelers would come looking for the city and believe they have taken a wrong turn, yet never being able to find it ever again.