A crossover could also involve a magical object from the Harry Potter universe being related to the Jack the Ripper case. Maybe the Ripper was after a powerful magical relic that was hidden in muggle London. Harry and his friends would then have to find the relic before the Ripper does, to prevent him from using its power for evil purposes.
One interesting crossover could be a situation where Jack Sparrow stumbles upon Hogwarts. Maybe he's looking for some magical treasure hidden there. He'd be completely out of place among the wizards and witches, and his roguish ways would likely cause all sorts of chaos and confusion.
Well, it could be a really dark and twisted story. Maybe Harry accidentally summons Jack the Ripper while trying out a new and powerful spell. Jack the Ripper's presence in the wizarding world would cause chaos. He might start attacking wizards and witches, thinking they're just like his normal victims in the muggle world. The Ministry of Magic would have a hard time dealing with him as he's from a different era and has a very different and brutal modus operandi.
Often, it's through creating a new villainous character inspired by Jack the Ripper. This character might have similar modus operandi but with a magical twist. For example, using a magical blade that leaves no trace.
Well, it's rather inappropriate. The Harry Potter universe is about magic, friendship, and heroism. Jack the Ripper represents a completely different and very dark aspect of human history. Mixing the two seems like a disrespect to the original themes of the Harry Potter series and also a rather morbid idea in general.
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.