Who would be the main antagonist in a 'harry meets tracer fanfiction'?

It could be a dark fairy who wants to use the power of both the wizarding world and Pixie Hollow for her own evil purposes. She might try to steal the magic from Hogwarts and the pixie dust from Pixie Hollow to become all - powerful.

Maybe the main antagonist could be Ra's al Ghul. He's always interested in power, and if he got his hands on some magic from the Harry Potter universe, he could become an even greater threat. He could try to use the magic to bring about his vision of a 'perfect' world, which would be at odds with both Harry's and Nightwing's ideas of justice. So they'd have to join forces to stop him from achieving his goals.

It could be a powerful dark wizard from Harry's world who has escaped into Wednesday's world to hide and cause chaos. This wizard might be attracted to the darker and more accepting atmosphere of Wednesday's world and use it as a base to plan his evil deeds. He could try to use the strange and spooky elements in Wednesday's world to create powerful dark magic, and Harry and Wednesday would have to join forces to stop him.

It could be a descendant of a rival family to the Peverells. This person might be jealous of the power and secrets that the Peverell family held and wants to stop Harry from uncovering them. They could try to manipulate events to their advantage and create obstacles for Harry.

It could be Aku. Since he is the main villain in Samurai Jack's world, his power and evil nature would make him a great antagonist. He could see Harry's magic as a threat and try to eliminate him. And if he teams up with some of the dark forces from the Harry Potter universe like Voldemort or the Death Eaters, it would be even more challenging for Harry and Jack.

There could be a group of dark wizards who are working together to bring chaos to the wizarding world. They target Amelia Bones because of her position in the Ministry and Harry Potter because of his fame. This group, with their evil intentions and powerful dark magic, would serve as the main antagonists in the fanfiction.

It could be Voldemort who somehow manages to cross over into the Star Wars universe. He might see the power of the Force as something to be harnessed for his own evil purposes. His dark magic would be a great contrast to the light - side teachings of Yoda, and Harry and Yoda would have to team up to stop him.

It could be the Red Queen. She might see Alice's presence in Mirana's world as a threat to her own power and try to stop their friendship.

A powerful witch coven might be the main antagonist. They could be jealous of the power that Klaus and Landon possess together. The witches might try to use dark magic to separate them and steal their powers for themselves. Maybe they have a prophecy that says the union of Landon and Klaus will bring about a change in the supernatural power balance that they don't want.

A possible main antagonist could be a powerful dark wizard who has somehow learned about the existence of the demigod world and wants to harness the power of the demigods for his own evil plans. He could be jealous of the unique abilities that Percy and Annabeth possess and see them as a threat to his rule in the wizarding world.