I have another candidate:
What's the work?
The Lion Guard, a show that was set in between the events of the Lion King films.
Who is He/What Has He Done
Ushari, a cobra. In the first season, he lived in the Pridelands and was neutral. In the second season, he grows tired of Bunga of the Lion Guard causing problems for him, so he leaves the Pridelands to go to the Outlands. In the Outlands, he encounters Janja and his clan, who prepare to eat him. Ushari tells Janja that if they work together, they can take over the Pridelands, revealing that he had discovered a way to summon Scar (Disney)'s spirit. The two manage to summon Scar's spirit so he can help them take over the Pridelands, betraying his entire land just so he can get into a position of power and take revenge on Bunga.
After Scar is summoned, Ushari becomes his second in command, doing everything he can to aid in Scar's plan. First, he convinces Kiburi to try and take over the Pridelands. When Kibiru fails and he and his crocs are banished, Ushari introduces them to Scar, who explains his plan to take over the Pridelands.
Later on, when Janja and his clan are unable to steal watermelons (to cause the elephants to run out of food and die) due to the interference of the Lion Guard, Ushari mentions his friend Kenge, saying he can paralyze the guard and allow the hyenas to steal the melons, ensuring the deaths of the elephants. Though this fails, Ushari continues to help Scar.
Ushari next aides Scar in his plan to kill Simba by getting him stung by a scorpion. When the Lion Guard arrive in the Outlands looking for a cure, Ushari reveals that he has been working for Scar and has all the Outland animals attack the Guard and Rafiki's new apprentice, Makini in an attempt to kill them. This fails, and the Guard and Makini escape and cure Simba.
During the season 3 opener, Ushari is at his worst. He informs Scar (after getting word from his skinks) that Janja was considering reforming. Scar decides to kill the entire hyena clan along with Simba, Nala, Kiara, Kion, and the rest of the Lion Guard. Ushari eagerly helps with this plan. Later, Ushari learns of Scar's plan to cause a volcanic eruption so the entire PrideLands will be destroyed by lava, allowing Scar and his followers to rule over the destroyed land after everyone is dead. Ushari and a couple of his skinks are the only ones to learn of this plan, yet Ushari continues to aid Scar after he promises Ushari he can take whatever he wants from the destroyed PrideLands. Ushari hides himself when the Lion Guard reach the lair, attacking Kion on Scar's command and infecting him with his venom, knowing that it will slowly drive Kion to madness. Scar and Ushari than mock Kion in an attempt to get him to use the Roar of the elders to cause the eruption. Kion however tells Scar that he forgives him and summons the spirits of the lions of the past to pass judgement on Scar. The spirits cause spiritual rain to wash away Scar's fiery spirit and destroy him forever. Enraged at having their plan to take over the PrideLands foiled, Ushari tries to kill Kion in a final act of spite. Bunga jumps in and stops him, causing them both to fall down into the volcano. Ono flies down and saves Bunga before he hits the lava, but Ushari isn't so lucky.
Freudian excuse/mitigating factors
Ushari's reason for turning evil was that he was sick of Bunga causing problems for him and wanted to gain more respect and power. Honestly though, extending his hatred of Bunga onto the entire PrideLands is crazy. Bunga may have done some mean things to him, but it's very hard to feel any pity or sympathy for Ushari when his response was to murder the entire PrideLands with Scar. It should also be noted that Kion was actually pretty nice to him. In one episode, Kion tells Bunga to leave Ushari alone and repeatedly checks in on Ushari to see how he's doing. How does Ushari repay Kion? by trying to kill him and his friends and family, ultimately going on to infect Kion with his venom that would slowly drive Kion to madness and turn him evil like Scar.
When he first proposed the idea of summoning Scar's spirit, it was in an attempt to avoid being eaten by Janja and his crew. However, afterwards, Ushari proves himself to be very sadistic, willingly aiding in Scar's plans. He is ultimately the only one of Scar's followers who does not reform and remains evil. In short, he takes his beef with Bunga way out of proportion and continues being evil even after ensuring his own safety is no longer a concern. His being labeled as a tragic villain is incorrect. He did have some bad things happen to him, but his actions are too heinous to make him sympathetic. In my opinion, that category should be removed from his article.
He refers to Kenge as his friend, but we don't actually see any real evidence of this other than them knowing of each other.
After Scar, Ushari is the most heinous villain in the LK franchise. He personally orchestrated Scar's resurrection, ultimately making him responsible for all the bad things that followed. While working for Scar, he proved himself to be very sadistic. He played a big part in Scar's schemes, and was ultimately the one who gave Scar the idea to kill the entire hyena clan after Janja, and only Janja, had been considering reforming. He and his skinks are also the only ones who knew about the plan to cause a volcanic eruption to kill everything in the PrideLands, yet he continues to help Scar. He's also the one who gives Kion his scar that ends up slowly driving him to madness. Finally, he's the only one of Scar's followers who does not reform. While he does not measure up to Scar himself, he's a close second. He took part in trying to starve a bunch of elephants to death, trying to kill the Lion Guard and their family and friends multiple times, and ultimately kicked off the plan to betray and murder Janja and his entire clan. Finally, he plays a central role in the attempt to kill everyone in the PrideLands. All this simply because of Bunga being a jerk to him. He does the absolute most with his resources.
In truth, regarding Scar's crimes strictly in the Lion Guard show, he and Ushari are about even in terms of heinousness except for Scar's act of killing the other four members of his lion guard. Scar and Ushari both run everything in the Outlands together, with Ushari acting as Scar's advisor and being the one who brought him back. The only thing apart from his movie crimes that puts Scar above Ushari, is his killing of his own lion guard teammates. Even than, that action, as well as his movie actions, can be explained by Scar having more resources.
Ushari is the worst villain in the franchise after Scar. He is responsible for all the conflict in seasons 2 and 3, and he is responsible for the show getting darker and more serious. He is a sadist, an ungrateful traitor, and an attempted mass murderer. He's also the first villain in a Disney Junior show to die. While not at the level of Scar, that is a case of resources. He does the most that he can with his level of power. I see no reason he shouldn't be voted a keeper.