There could be new villains like an evil wizard - scientist who wants to use magic to create black holes and destroy planets for his own gain. Or perhaps an alien race that has a natural ability to drain magic from wizards and witches and they see the Hogwarts students as a source of power.
There could be alien dark wizards. They might have their own brand of magic that is different from what Harry is used to on Earth. They could be trying to steal Earth's magic for their own evil purposes.
One possible main villain could be an Egyptian wizard who has been corrupted by dark magic. He might be after some powerful Egyptian artifact that can give him ultimate power. He could see Harry as a threat to his plans because Harry has knowledge of different kinds of magic from Hogwarts.
It could be Death Eaters who have a new plan. They might want to create chaos in the Muggle world by targeting the Queen. They see her as a symbol of Muggle power and order, so by attacking her, they hope to disrupt the Muggle - wizard relationship.
The Malfoys could be the main villains. They might have turned to even darker magic after the fall of Voldemort and formed their own secret organization. Lucius Malfoy could be using his wealth and influence to gather dark wizards and witches to create chaos in the wizarding world.
It could be some Death Eaters who have made a deal with a Wakandan traitor. They might want to steal Wakanda's vibranium to make powerful dark magic items. The Death Eaters' dark magic would pose a serious threat to Wakanda's peace and stability.
The Death Eaters could also be major villains. They might team up with some anti - SHIELD groups in the muggle world. The Death Eaters' dark magic combined with the muggle - world weaponry of these groups could pose a serious threat to both the wizarding and muggle worlds that Harry and SHIELD have to stop.
Well, in such a fanfiction, he might control space through his magic wand. Maybe he uses a special spell that he discovers or invents, which allows him to manipulate the fabric of space, like creating portals or warping distances.
His personality would likely be more cold and calculating. He'd be used to getting his way through underhanded means taught by the villains.
Voldemort would still be a likely villain. He is the main antagonist in the original series and his threat to Harry is always present. Even if Harry is trying to save himself, Voldemort's power and his desire to kill Harry would make him a formidable foe.
In this kind of fanfiction, Harry might grow up with a very different set of values. He could be trained in dark magic or used as a tool by the villains. Maybe he would be more cynical and less trusting compared to the original Harry. For example, if he was raised by the Death Eaters, he might be taught to hate Muggles and Muggle - borns from a young age.