The Ancient Spirits of Evil themselves could also be antagonists. They might not trust Cheetara and constantly test her loyalty. They could send their own minions to spy on her and try to make her fail in her tasks for Mumm - Ra. This would make Cheetara's situation even more complex as she has to deal with not only Mumm - Ra but also these powerful and distrustful spirits.
Another possibility could be Monkian. He might suspect that Cheetara is not fully loyal to Mumm - Ra and start his own investigation. His actions could put Cheetara in danger as she is already in a difficult position as a servant. And if he finds out the truth, he could expose her to Mumm - Ra, which would be a huge threat.
Perhaps in the fanfic, Cheetara becomes Mumm - Ra's servant due to a spell. Mumm - Ra uses her to steal a powerful artifact from the Thundercats. But during her mission, Cheetara has flashbacks of her time with the Thundercats and their friendship. This makes her have second thoughts and she tries to find a way to break free from Mumm - Ra's control while protecting the artifact from falling into his truly evil hands.
One possible plot twist could be that Cheetara discovers Mumm - Ra's true nature only after the marriage. Maybe she thought she could change him, but then realizes he has some dark ulterior motives that put her and her friends in danger.
The other characters would likely be very shocked. For example, Lion - O, who might have had feelings for Cheetara, would be heartbroken. And the Thundercats as a whole would be distrustful of Mumm - Ra and might see Cheetara as a traitor.
In a fanfiction, the Naruto - Mumm - Ra fusion could be described as a being of contradictions. It would have Naruto's kind heart warring with Mumm - Ra's evil intentions. Physically, it could be like a mummified ninja, with Naruto's features distorted by Mumm - Ra's presence. Its abilities would be a chaotic combination. It could use Naruto's shadow clones but with a dark twist from Mumm - Ra. And when it uses its power, there could be a mix of Naruto's bright chakra and Mumm - Ra's inky black energy.
It could be the person or group who sent the troll. Maybe there's a mastermind behind the troll's actions, like a villain who wants to distract Bucky from something important. So while the troll is the immediate target of Bucky's punch, the real enemy is the one pulling the strings.
The opera house owner could be a main antagonist. He might be more concerned with money and his own reputation than the well - being of the performers. He could try to stop the Phantom's attempts to improve the opera, seeing it as a threat to his control.
A new supervillain could be introduced, like a mad scientist who has developed a device that can nullify superpowers. He could target the Incredibles specifically because they are the most well - known superhero family, and wants to prove that his technology is superior to superpowers.
If Naruto and Mumm - Ra fused, it could result in a very unique appearance. Naruto's spiky hair and orange jumpsuit might mix with Mumm - Ra's skeletal and mummified look. In terms of powers, Naruto's Rasengan could potentially be infused with Mumm - Ra's dark energy, creating a super - powerful and dangerous attack. This fusion would also likely have a complex personality, as Naruto is generally upbeat and Mumm - Ra is full of malice.
Rose Granger - Weasley could also be a main character. Given her intelligence and her family's history, she could play a crucial role. She might be the one who discovers some important clues about the servant of Nagini through her research in the Hogwarts library. And she could use her magical skills, which she has inherited from her parents, to assist Albus and others in dealing with the servant.
It could be another powerful god or goddess who wants to use Percy's betrayal of Tartarus for their own gain. Maybe a god of chaos who sees this as an opportunity to create more disorder in the world. They might manipulate Percy into the betrayal and then turn on him later.