In some fanfiction, there could be a plot where the characters from both universes team up to fight a common enemy. For example, the Death Eaters and the Huns could form an alliance, and then Harry, Mulan and their friends have to combine their strengths. Mulan's leadership and Harry's magical abilities would be crucial in this fight.
One interesting crossover could be Mulan attending Hogwarts. Imagine her bringing her martial arts skills to Defense Against the Dark Arts class. She could teach the students some unique combat moves.
One idea could be that Mulan is a transfer student to Hogwarts. She could bring her unique martial arts skills and sense of honor to the wizarding world. Maybe she'd be sorted into Gryffindor for her bravery. Another idea is that Harry Potter somehow gets transported to Mulan's world and has to learn how to fight like a warrior there, using his magic in new and unexpected ways.
One interesting crossover could be the Quirk vs Magic aspect. In many bnha harry potter fanfictions, characters from BNHA like Deku might visit Hogwarts and try to understand magic while the Hogwarts students are fascinated by his Quirk. It makes for a great exploration of two very different power systems.
One interesting crossover could be the use of magic systems. In some fanfictions, the characters might combine spells from Harry Potter with the dragon - related magic in Eragon. For example, a wizard from Harry Potter might learn to communicate with dragons like the characters in Eragon.
One interesting crossover could be Ben using his alien forms to help the students at Hogwarts during a dark wizard attack. For example, his Heatblast form could be useful against ice spells. Another could be Harry Potter using magic to enhance Ben's Omnitrix. Maybe a spell that makes it transform faster or unlock new alien forms.
One interesting crossover could be the use of magic from Harry Potter in the RWBY universe. For example, a character from RWBY might learn how to use spells like Wingardium Leviosa to help in combat or daily tasks. Another could be the Hogwarts houses being applied to RWBY characters, with Ruby perhaps being a Gryffindor due to her bravery.
In some Harry Potter and Riverdale fanfiction, the houses in Hogwarts could be compared to the social groups in Riverdale. For example, Gryffindor's bravery could be related to how the Bulldogs in Riverdale stand up for what they believe in. Slytherin's cunning might be similar to how some of the more devious characters in Riverdale operate. And then there could be a plot where characters from Riverdale are sorted into Hogwarts houses and have to adapt to the new environment based on the traits of their houses.
In Harry Potter and Clannad fanfiction, a great crossover idea is the exchange of character traits. Maybe some of the Clannad characters could be sorted into Hogwarts houses based on their personalities. And vice versa, the Hogwarts students could learn about the strong family and friendship bonds in Clannad. It could also involve a plot where a powerful Clannad character has to deal with the dark magic threats in the Harry Potter universe. This would create a whole new set of challenges and adventures for both sets of characters.
One interesting crossover could be the use of magic systems. For example, how would the Shadowhunter runes interact with Harry Potter's spells? Maybe a character from the Shadowhunter world could find themselves at Hogwarts and be both amazed and confused by the different forms of magic. Another aspect could be the characters' personalities clashing or working together. A brave Gryffindor and a fearless Shadowhunter might team up to fight a common evil that threatens both their worlds.
One interesting aspect could be the contrast in magic systems. In Harry Potter, magic is more about spells and potions, while Starscream has his own set of technological 'powers' in the Transformers universe. A crossover might explore how they interact. For example, how would Starscream react to a wizard's ability to apparate? And how would a wizard deal with Starscream's flight and weaponry capabilities.
In Harry Potter and The Flash fanfiction, a common theme is the exploration of different forms of transportation. The Flash's super - speed is a form of getting around quickly, while in Harry Potter, they have brooms, Portkeys, and the Floo Network. A fanfiction could explore how the Flash would react to these magical means of travel. Maybe he'd be impressed by the idea of flying on a broom or find the Floo Network's green flames a bit strange. And on the other side, Harry Potter characters could be amazed at how the Flash can run across water or up the sides of buildings just by using his speed.