I wanted to propose this villain since last year. The Witch that possessed Azkadellia, in Tin Man.
What is the work?
Tin Man is a Oz based tv miniseries that is supposed to takes place and time several years after the original Dorothy Gale's story. It follows the story of her descent, DG, who was one of the princes of Oz, but had forgotten this after she was killed by her sister and revived by her mother. Her sister in question, Azkadellia, runs Oz as a evil magical ruler after had take it from her parents after being possessed by an ancient, evil witch, which is our candidate in question.
Who is she and what she did?
The Wicked witch is a ancient, demonic 500 years old evil witch who lived trapped in a cave until the young Azkadellia, along with her younger sister, DG, the protagonist of the series, entered this cave being attracted by the cry of a child only to discover that the "child" was a decrepit witch who had taken the form of a little girl in order to attract them. The witch realized the magic between Azkadellia and her sister was very strong and asked the two of them to let go, using the fear of the girls. Prudent, Azkadellia refused to let go of her sister and told her that they should be together, but the fear the witch instigated in DG was stronger, causing the younger sister to flee, leaving the older sister to be possessed by the witch, turning Azkadellia into the main antagonist of the story.
Little is known about the back story of this witch, but that she was an inhabitant of Oz who was imprisoned in the cave for practicing black magic, terrorizing the people and spreading chaos. Besides that is known is that she is behind all the evils committed by Azkadellia, since she possessed this, in order to use it as a means to conquer Oz and all the other worlds. I will describe the main acts of the witch commited while possessing Azkadellia's body.
Before the incident, Azkadellia was an innocent and good girl who loved her family and was happy with them. But after the witch's possession, she control her to try to kill his own sister, making her loose the memoir and magical powers, and became the main antagonist, also expelling her parents from Oz and locked them into a pocket dimension, and becoming a tyrant ruler, turning Oz into a dystopian tirany, with smart people being lobotomized, in order to Azkadellia use their brains; having places, including the forest where she and DG found the witch, burned; slaved the race to which the lion belongs, known as "Veiwers" or Raw's people, with their psychic powers extorted from their minds agonizingly; and torturing or killing any opposite to the regime, with the worst setence is locking the opposite into a rusty suit of armor unable to move until their deaths. She also had the life of the Mystic man drained, causing his death.
The final plan of the Witch, under Azkadellia desguise is to use an eclipse to cause eternal darkness on Oz, which will destroy all life on Oz, using a machine called Anti-Sun Sedder, which was used as a Sun-Seeder for agricultural proposes. At a moment, the Witch/Azkadellia looks DG into a coffin after taking the emerald she will use to cause the eclipse from her. Using magic to release herself, DG manages to get into the Azkadellia fortress and achieves to conciliate with her, ultimatelly releasing the wicked witch from Azkadellia's body. After trying to kill DG and Azkadellia, plus giving the eternal eclipse, the witch is destroyed and Azkadellia is a good person again.
Although Azkadellia showed to be the main antagonist, the show makes it clear that she was only under the witch's control and possession, and everything she did and wanted to was not actually her will and plans, but the wicked witch's. If Azkadellia showed to be sufficient heinous, all of this is actually from the witch, not by Azkadellia herself. We don't know much about what the witch did in the past, but we do know what she got Azkadellia to do and what she was planning for Oz and the rest of the worlds. Behind everything the witch did while possessing Azkadellia body and considering the sorceress' final plan was to bring eternal darkness and destruction to Oz, she is indeed an interesting candidate, since she is the real author of all "Azkadellia's wickedness" and being the main antagonist, leading her to almost murder her own sister, which is also pretty heinous.
Screen-time: The witch herself only appears in two moments: when Azkadellia and DG found her on the cave and she possessed the first; and when she was disassociated from Azkadellia at the end, prior to her defeat. However, considering the fact she was the true one menifest throught Azkadellia's body and that was she, not Azkadellia herself, that was doing all of that evil, I think that, possessing Azkadellia and being the one behing her acts, she had suficient screentime to qualifies. Further, there's no mitigating factors, redemming qualities, and the little we can know about the witch's backstory indicate she was a people with moral agency, not something made of evil.
She gets a yes from me. While Azkadellia obviously can not be Pure Evil, the witch that possessed and controled her into becoming evil and doing all of such awfull things certainly qualifies.