*Thinking contemplatively*
What is the work?[]
This does not need much explanation. Return to Oz was Disney's attempt at making a series based on the Land of Oz books and serves as a semi-sequel to the 1939 classic musical film. Except here, there are no songs. No whimsical, childlike joy of being isekaied into another world by the distant cousin of Truck-kun, Tornado-kun.
Instead, Dorothy finds the Yellow Brick Road desecrated and the Emerald City made bare with all its citizens transformed into stone statues. And some nightmare fuel-inducing freaks known as the Wheelers. Who, or what has abominated the Land of Oz into this hellish state? He is the candidate for today.
Who is he? What has he done?[]
Upon leaving Oz, the Nome King finds Dorothy's Ruby Slippers and uses their power to usurp the Scarecrow and take over Oz transforming nearly all its inhabitants into stone (at the least the Cowardly Lion and Tin Woodsman went down fighting). He then arranges for the vile woman Princess Mombi to become his right-hand offering her a deal of 30 fresh heads of young women in return for her keeping the true ruler of Oz, Ozma, captive.
When Dorothy returns to Oz and sees it in ruins with the Emerald City stripped of its pretty jewels, she confronts the Nome King who explains to her that all the precious jewels were rightfully his and that the people of Oz stole them to make their extravagant Emerald City (though of course he is a liar since the jewels were there before the Scarecrow took over in Ozma's absence). Being the sadistic kind of guy he was, he suggests a game to Dorothy and her friends: each one would go into a room filled with green ornaments those being all the Oz civilians he had imprisoned.
With the game, each one had three chances to figure out where the Scarecrow is. Little do they know, once they turn into ornaments, the Nome King would take on a more human-like appearance before eventually breaking free of his limitations to become even more powerful. So he is essentially feeding off their lives. All of Dorothy's friends fail, but Dorothy is able to find the Scarecrow if only barely.
The Nome King becomes enraged that he was being reabsorbed into stone and becomes a giant behemoth and tries to eat everyone. But as he approaches Jack Pumpkinhead, who was Dorothy's "son" as he so called, the Nome King screws up unaware that Bilina, a hen that was taken into Oz alongside Dorothy (and can talk...why didn't Toto talk), lays an egg which falls down his gullet.
The film earlier foreshadowed and later confirms that eggs were poisonous to Nomes. As such, the Nome King crumbles in agony while the heroes escape. With his reign put to an end and Ozma once more in her rightful place, Dorothy returns home learning that the mental institution was struck by lightning and burned to the ground.
Freudian Excuse? Mitigating factors?[]
He claims that he took over Oz and stripped the Emerald City of its jewels as revenge for stealing all his jewels. However, this is hardly a justification for petrifying everyone. Instead, the movie depicts him as a greedy scrooge with his jewels.
As for Dorothy, when she starts crying and he seemingly takes pity on her and comforts her. However, the novelization of the film makes it clear that he was faking sympathy and actually took relish in her suffering. Even if you are willing to believe that it was genuine, he was fully intent on making her into an ornament and hoped she would lose her three guess attempts. That, and him trying to eat her and everyone else when he was raging out.
So, some had wondered on how he gently puts Jack Pumpkinhead and the hen down after discovering he had royally screwed up by ingesting the egg, concluding that it was a Pet the Dog moment. With that, I also feel this is easy to debunk: not only was he going to enjoy devouring them one by one, but Dorothy and the gang were trapped in his collapsing lair and narrowly escape. So even if he stopped pursuing them to kill them, the gang would have otherwise died in the crumbling lair.
Heinous standard[]
So, the turning of people into stone and ornaments aren't what I think puts him over since this could be considered generic. What does push him over, however, is the fact that Mombi collecting the heads of women was his idea to rope her into assisting him. So, yeah, he subjects several innocent women to an And I Must Scream fate with all the horrific implications coming with it.
But that does not disqualify Mombi not one bit since she is also the one who was imprisoning Ozma and tried taking Dorothy's head as well.
As for Dr. J.B. Worley, I think he is fine to stay. He is a human quack doctor after all who had destroyed several of his patients' minds with his machines and tried doing the same to Dorothy. He has his own niche he inhabits.