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 Harry Potter RWBY fanfiction, there could be a crossover where the Deathly Hallows play a role in the RWBY world. Maybe the Elder Wand could be found in Remnant and it gives the wielder some extraordinary power. And the Sorting Hat could be brought to RWBY's Beacon Academy and start sorting the students there based on their personalities, just like in Hogwarts. This would create a whole new dynamic in the RWBY story.
Well, a cool crossover in Harry Potter RWBY fanfiction could be the appearance of RWBY characters at Hogwarts. Picture Weiss in her school uniform walking through the halls of Hogwarts, or Yang getting into a friendly duel with a Gryffindor student. It would be really fun to see how RWBY's weapons and fighting styles interact with the magic and rules of Hogwarts.
Well, a cool crossover might involve the Grimm from RWBY being affected by the magic in Harry Potter. Maybe the Death Eaters could team up with some of the more evil forces in RWBY. Also, the different houses in Hogwarts could be compared to the teams in RWBY. For instance, Gryffindor's courage could be related to Team RWBY's fearless nature.
A really interesting crossover is when the Grimm from RWBY are introduced into the Harry Potter world. Imagine the Hogwarts students having to face these dark and menacing creatures. It makes for some intense battle scenes and a great combination of the two worlds' combat styles.
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.
One interesting crossover could be a scenario where Harry Potter and his friends encounter Janemba's chaotic powers in the wizarding world. Maybe Janemba's otherworldly abilities disrupt the magic there, and Harry has to use his knowledge of both magic and the strange new power he's facing to set things right. For example, he might combine spells with his natural courage to combat Janemba's minions.