In this kind of fanfiction, the main antagonists could be a combination of the traditional Harry Potter villains like the Death Eaters and new threats from the Marvel side. For instance, Dormammu could somehow sense Harry's potential and try to either possess him or destroy him to prevent him from becoming a powerful force against him. And of course, there would always be some wizards in the Harry Potter world who are against any kind of change or outside influence, and they could also oppose Harry.
The main antagonists could still be Voldemort and his Death Eaters. Just because Harry is being raised by Moriarty doesn't mean Voldemort's threat disappears. In fact, Moriarty might see Voldemort as either a rival or a potential ally, which would add another layer of complexity to the story.
It could be the Death Eaters still. But with Harry being raised by Revy, they might face a much more formidable opponent. Harry would have a different set of skills and a more aggressive approach, so the Death Eaters would have to adapt. Another possibility could be some of the more corrupt wizards in the Ministry of Magic who don't like this new, unpredictable Harry.
In this fanfiction, the Death Eaters would remain as antagonists on the wizarding side. They follow Voldemort's ideology and would oppose Harry no matter who raised him. But also, there could be elements from Jean Grey's world that turn against Harry. For example, if there are mutants who fear that Harry's magic could disrupt the balance between mutants and humans, they might become antagonists. It would add a whole new layer of conflict to the story.
In such a fanfiction, Harry Potter would probably grow up with a much different set of values. Doctor Strange is often about protecting the world from threats from other dimensions. So Harry could be trained to face threats that are not just from the dark wizards in his own world. He might also have access to some really cool artifacts from the Marvel universe. And his relationships with his friends would be different too. Instead of just Hogwarts classmates, he could have allies from different realms.
Voldemort would still be a major antagonist. But there could also be new threats emerging from the clash of the wizarding world and Zabuza's world. Maybe some dark wizards who are envious of Harry's unique upbringing and new skills would try to take him down.
It could be the same Voldemort as in the original series. But his approach to Harry might be different. Since Harry is being raised by Raven, he might be more difficult to target as he has different knowledge and skills. So Voldemort might have to come up with new and more devious plans to get to Harry.
Sauron could be a major antagonist. His power and desire for domination would put him in direct conflict with Harry. Voldemort - like elements might be incorporated into Sauron's character in this fanfiction.
There could also be some characters from the Doctor's universe who oppose the idea of a half - wizard, half - Time Lord. They might come to the wizarding world to try and stop Harry from using his combined powers, fearing it could disrupt the balance between the two universes.
Voldemort would still be a major antagonist. His goal of ruling the wizarding world and eliminating Harry Potter would remain. However, there could be new antagonists added due to Hawkgirl's presence. For example, some Thanagarian villains might follow Hawkgirl to the wizarding world and see the chaos Voldemort is causing as an opportunity to gain power for themselves. They could try to form an alliance with Voldemort or simply try to take over the wizarding world on their own.
It could be the Saiyans. In the Dragon Ball universe where Frieza exists, the Saiyans are often his enemies. Even if Harry is reborn as Frieza, the Saiyans' natural strength and warrior spirit would pose a great threat to him. They might not understand his new - found combination of magic and Frieza's powers and see him as an even greater danger.