Another possibility is that there is an ancient evil that Raven has been keeping at bay. But by raising Harry, this evil senses an opportunity. This antagonist could be something that was once sealed away long ago and now wants to use Harry's power (which has been shaped by Raven) for its own dark purposes. It could be an entity that is more powerful and mysterious than Voldemort, leading to a very different kind of struggle for Harry.
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.
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.
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.
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 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 Thalmor could be great antagonists. Their strict control over magic and their anti - human beliefs could put them at odds with Harry. They might see his different form of magic as a threat to their power in Skyrim.
One possible antagonist could be a corrupt wizard in a high - ranking position in the Ministry of Magic's financial department. This wizard might be trying to cover up his misdeeds and would see Harry as a threat to his scheme.
Raven could be an ancient and powerful witch who has been living in seclusion for centuries. She might have noticed Harry's special aura or his connection to powerful magic and decided to adopt him to pass on her knowledge.
Maybe there are some ancient dark wizards that Iskandr has a history with. These wizards could see Harry as a threat because of his potential, especially with Iskandr's training. They might emerge from hiding to try and stop Harry from reaching his full power, fearing that he and Iskandr together could disrupt their long - planned evil schemes.