The plot could involve a magical artifact that has the power to connect different magical realms. This artifact is being sought after by both Voldemort's followers in the Harry Potter world and an evil force in Moana's world. Moana and Harry Potter, along with their friends, must race against time to find the artifact first. During their adventure, they learn about each other's cultures and magics. For example, Moana shows Harry how to communicate with the ocean spirits, and Harry teaches Moana about the magic of Hogwarts. They end up using their combined skills to defeat the bad guys and protect the artifact.
One possible plot could be that Moana's island is threatened by dark magic from the Harry Potter universe. Harry, Hermione, and Ron could be transported to Moana's world while on a mission to stop the spread of this dark magic. They would team up with Moana to use her knowledge of the ocean and the island's magic, along with their own wizarding skills, to fight off the dark forces. Maybe they'd have to face off against a wizard who has enchanted some of the sea monsters in Moana's world.
In a Harry Potter - Moana crossover fanfiction, the magical creatures in the Harry Potter world could interact with the spirits in Moana's world. For instance, a Hippogriff could fly over Moana's island and be seen as a strange new creature. Or the Maui's fishhook could have some sort of magical connection with a powerful wand in the Harry Potter universe. The characters' personalities would also make for great combinations. Hermione's intelligence and Moana's determination could lead them to solve some big mystery together that involves both their worlds.
It could be really interesting. Maybe Harry Potter uses his magic to help Moana on her journey. For example, he could use a spell to calm the rough seas she sometimes faces. Or Hermione could use her vast knowledge to figure out some of the mysteries in Moana's world that even she doesn't understand yet.
A cool plot could be that a dark force from Naruto's world has found a way into Moana's world. Naruto, with his knowledge of fighting evil, and Moana, with her knowledge of the local terrain and the ocean, must work together. Naruto might be a bit clumsy at first with the whole sailing thing, but his combat skills are invaluable. Moana, on the other hand, can communicate with the ocean to get them out of tight spots, and together they defeat the dark force.
In a Harry Potter and Superman crossover fanfiction, perhaps Voldemort discovers Superman's existence and tries to use his powers for his own evil deeds. He might try to control Superman's mind. But Superman, being the strong - willed hero he is, resists. Harry and his friends then team up with Superman to fight Voldemort. They learn a lot from each other. Harry learns about physical strength beyond magic, and Superman gets to understand the complexity of magic.
One possible plot is that a dark magic from the Darksiders universe seeps into the Harry Potter world. Harry and his friends discover that the only way to stop it is to learn some secrets from the Darksiders. So they embark on a journey through both worlds, meeting various characters from each along the way and using a combination of magic and the powers of the Darksiders to combat the threat.
The plot could involve Maleficent's magic interfering with Hogwarts' protective spells. She might be on a quest to find a powerful magical artifact hidden in Hogwarts that she believes will make her even more powerful. Harry and his friends suspect her motives and start to investigate. In the process, they learn about Maleficent's past and find some similarities between her story and their own fight against the dark forces in their world.
Well, it could be that Supergirl lands in the wizarding world somehow. Maybe she's chasing a bad guy who uses magic to escape to Hogwarts. And then she teams up with Harry Potter to fight the bad guy. Harry could teach her about magic while she teaches him about her superpowers.
Well, perhaps the magical creatures from the Harry Potter universe end up in the '300' setting. Dragons could be used by the Spartans to fight their enemies. The centaurs could also join the battle, lending their archery skills. And Harry could learn some combat skills from the Spartans, which he could then use back in the wizarding world to fight Voldemort's Death Eaters.
One possible plot could be that the Flash accidentally runs into the wizarding world. He might be chasing a villain who has some sort of magic - based powers and ends up in Hogwarts. Harry Potter and his friends could be initially suspicious of this strange, super - fast man in a red suit. But then they realize they can work together. The Flash could use his speed to help in tasks like quickly gathering potion ingredients across the vast Hogwarts grounds, while Harry and his friends could use magic to help the Flash understand and navigate the complex magical world.
One possible plot could be that Aquaman somehow finds himself in the wizarding world of Harry Potter. Maybe a magical spell gone wrong transports him there. He could use his unique underwater abilities to help the Hogwarts students in a task related to the Black Lake, like retrieving a powerful magical artifact that has sunk to the bottom.