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.
Well, in some fanfictions, there are crossovers in terms of the settings. Imagine the Institute from the Shadowhunter world existing in the same realm as Hogwarts. Students from Hogwarts could visit the Institute and learn about the Shadowhunters' way of life, and vice versa. It would be really cool to see how the different cultures within these two fictional universes interact. And then there are the character relationships. A Shadowhunter might fall in love with a wizard or witch, which would create a whole new dynamic full of drama and adventure.
Harry Potter himself is quite popular. His status as the Boy Who Lived gives him a certain allure in the crossovers. Fans like to imagine how he would handle the different threats in the Shadowhunter world. Clary Fray is also a favorite. Her journey as a Shadowhunter, especially her discovery of her powers, can be paralleled with Harry's discovery of his wizarding abilities. And when they interact, it can lead to some really engaging storylines.
One interesting fanfiction could be about a crossover where the magic systems of both worlds collide. Maybe a Shadowhunter ends up at Hogwarts and has to adapt to the very different magical environment there. Another could involve a joint quest where characters from both universes team up to fight a common enemy, like a powerful dark wizard who has somehow gained access to the Shadow World's demons.
The crossovers that involve the main characters from both series are often the most interesting. For instance, when Clary from Shadowhunters is a tribute in the Hunger Games. Her ability to create new runes could potentially give her a unique advantage in the arena.
Well, in some fanfiction, we might see Anna and Kristoff visiting Hogwarts. They could be amazed by the moving staircases and magical creatures. In reverse, Harry, Ron and Hermione could end up in Arendelle. Hermione might be intrigued by the way Elsa controls her ice powers and try to find a scientific or magical explanation for it. Also, the Dementors from Harry Potter could be compared to the dark forces in Frozen 2, like the mist that Elsa has to face.
One interesting crossover could be the use of magic in the Avengers world. For example, Hermione could use her knowledge of spells to help the Avengers solve a problem that technology couldn't. Maybe she could use a spell to break through an impenetrable force field created by an enemy. Another aspect could be the Avengers characters learning magic. Tony Stark might be fascinated by the concept of magic and try to incorporate it into his technology. Or Thor could share his knowledge of Asgardian magic with the Hogwarts students.
One interesting crossover could be a scenario where Hermione uses her magic to help Elsa control her powers better. Maybe she creates a spell that can soothe Elsa when she's about to lose control.
In some fanfiction, Maleficent might team up with a dark wizard from the Harry Potter universe. They could combine their powers to try and take over both the wizarding world and the fairy - tale land where Maleficent comes from. This would create a complex power struggle with the heroes having to find new ways to combat them.
One interesting crossover could be the characters from Harry Potter visiting Narnia. For example, Harry, Ron, and Hermione might find themselves in Narnia through some magical accident. They could then interact with the talking animals and magical beings there, like how they interact with the magical creatures in their own wizarding world. Maybe they would help the Narnians in a battle, using their unique Hogwarts - taught magic.
One interesting crossover could be the use of spells. For example, a Charmed one might learn a spell from the Harry Potter world like the Patronus charm. It could be used in a new and different way in the Charmed universe, perhaps to fight a new type of demon that is vulnerable to positive magic like a Patronus.
One interesting crossover could be Superman visiting Hogwarts. He might be amazed by the magic there. Maybe he tries to learn some spells, but his superpowers interfere. For example, when he tries to use a levitation charm, his super strength makes the object fly out of control.