One idea could be to have a wizard from the Harry Potter world time - travel to the Tudor era. Maybe they get mistaken for a sorcerer or a prophet. Another could be to have a Tudor character discover a hidden wizarding school in England during that time. They could then learn some basic magic and use it to their advantage in the Tudor court politics.
One interesting concept could be the merging of the magical world of Harry Potter with the historical context of the Tudors. For example, how would the wizarding laws and society interact with the Tudor monarchy? Maybe there are fanfictions where wizards have to hide their magic more carefully during the Tudor era to avoid persecution from the Muggle rulers. Another concept could be characters from Harry Potter being placed in Tudor - like situations. Like Hermione using her knowledge to navigate the complex politics of the Tudor court while still being a witch.
One idea could be that Merlin somehow gets transported to the Harry Potter universe. He could use his magic, which is different from the wizarding magic in Harry Potter, to solve some of the mysteries or problems there. Maybe he teams up with Harry and helps him defeat Voldemort in a unique way, like using his ancient magic knowledge.
One interesting idea could be a crossover with a fairytale world. For example, Hermione could be transported to a world like Cinderella's and meet a prince who has some magic similar to that in the Harry Potter universe. This would create a new kind of romantic dynamic where she has to balance her Hogwarts knowledge with this new, more traditional fairy - tale romance.
One idea could be that Hogwarts students discover Pokemon in the Forbidden Forest. They could start training them as part of a new magical - creature - handling class. Another idea is that a powerful Pokemon like Mewtwo ends up at Hogwarts and causes chaos among the students and teachers, who have to use their magic to deal with it. Also, a wizard could accidentally cast a spell on a Pokeball and create a new, hybrid Pokemon - magic creature.
In a Bleach and Harry Potter crossover fanfiction, it could be fascinating if the Quidditch players in Harry Potter had to face off against Hollows during a game. Imagine the chaos! Or perhaps the magic spells in Harry Potter could be used to enhance the powers of the Soul Reapers in Bleach. For example, a spell could be used to strengthen the bond between a Soul Reaper and their Zanpakuto. And if the Triwizard Tournament had a special task where the contestants had to team up with a Bleach character to defeat a powerful combined threat of a Dark wizard and a powerful Hollow.
In a crossover, the underworld could have its own form of magic that is different from the magic in the wizarding world. Ron could be the one to first discover a connection between the two magics. He might find an old artifact in the wizarding world that has a link to the underworld. This could lead to an adventure where the trio explores the underworld to prevent a dark magic from the underworld from spreading into the wizarding world.
One idea could be to have the Gallagher family from 'Shameless' somehow end up at Hogwarts. Maybe Fiona could be mistaken for a new teacher and cause chaos in the school with her no - nonsense attitude. Another could be Lip getting involved in a magical experiment gone wrong with Hermione. He might use his street - smart knowledge to help her out in a different way than she's used to.
Perhaps the BTS members are magical creatures in the Harry Potter universe. Jin could be a Veela, with his good looks and charm that can sometimes entrance people, much like the Veela's allure in the books. Suga could be a Kneazle, independent and with a sharp mind, able to sense things others can't, just as he often has a unique perspective in his music - making. And they could all be on a quest to find a special magical object that has the power to combine the magic of their world (the BTS world) and the wizarding world of Harry Potter, and along the way, they meet Harry, Hermione, and Ron and form an unlikely alliance.
Perhaps there could be a magical object in 'Harry Potter' that is somehow related to the werewolves in 'The Howling'. For example, a spell book that has the secrets to controlling werewolf transformations. The characters from both worlds could be on a quest to find this book and in the process, they learn more about each other's worlds and how magic works differently in each.
One idea could be that Hermione Granger somehow gets transported to the world of Tangled. She could use her magic to help Rapunzel understand the true potential of her long hair, perhaps in a more scientific way. For example, Hermione might discover that Rapunzel's hair has some sort of magical core similar to a wand. Another idea is that the Dementors from Harry Potter somehow end up in the Tangled world. Rapunzel, with her positive and strong - willed nature, could be one of the few who can resist their soul - sucking powers and then teach others in her world how to do it. And maybe Harry Potter himself could be on a quest in the Tangled world, looking for a magical object that is said to be hidden there, and he teams up with Flynn Rider and Rapunzel to find it.