One possible plot could be that Mulan is magically transported to the wizarding world of Harry Potter. She could be mistaken for a new student at Hogwarts and placed in Gryffindor due to her courage. Then, she uses her martial arts skills to help the students in Defense Against the Dark Arts class. Maybe she teams up with Harry, Hermione, and Ron to face a new dark threat that is a combination of the magic in the wizarding world and some ancient Chinese magic that has somehow seeped into Hogwarts.
Perhaps Mulan is sent to the wizarding world on a mission from her own land. She arrives at Hogwarts disguised as a male student (like she did in her own story). She quickly catches the attention of the Golden Trio. Harry might notice something different about her and as they get to know each other, they discover that there are dark forces in both their worlds that seem to be connected. Mulan could teach the Hogwarts students some of her military strategies, and they in turn could help her understand magic better so they can all fight against the common threat.
Mulan and Hermione would be a great pair. Hermione is known for her intelligence and thirst for knowledge, while Mulan is brave and resourceful. They could learn a lot from each other. Hermione could teach Mulan about magic theory, and Mulan could show Hermione some of her combat skills and how to think outside the box in difficult situations.
Well, perhaps the magical creatures from the Harry Potter universe end up in the '300' setting. Dragons could be used by the Spartans to fight their enemies. The centaurs could also join the battle, lending their archery skills. And Harry could learn some combat skills from the Spartans, which he could then use back in the wizarding world to fight Voldemort's Death Eaters.
Mulan's strong leadership skills would shine in the wizarding world. She might lead a group project in Hogwarts, much to the surprise of some students who are used to more traditional leadership. Harry would see in Mulan a kindred spirit in terms of facing challenges. They would bond over their shared experiences of being different and having to prove themselves. Mulan would also interact with the house elves, and her kindness and respect for all beings would endear her to them. She could teach them some of her own cultural values, while they could introduce her to the unique magic of Hogwarts' kitchens.
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 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 possible plot could be that the Smurfs accidentally find a magical portal that leads them to the wizarding world of Harry Potter. They could be initially confused but then start to explore. Maybe they meet Hagrid, who is fascinated by these small blue creatures. The Smurfs could use their unique skills, like Papa Smurf's potion - making skills, which could be a new and interesting concept in the wizarding world. And they could also get involved in some of Harry's adventures, helping him out in their own little ways.
One idea could be that Carly and her friends discover a magical portal in their apartment that leads to Hogwarts. They then have to navigate the wizarding world, with Carly being fascinated by all the magic. Meanwhile, Harry Potter and his friends are intrigued by the strange Muggle - like devices the iCarly gang has. They end up teaming up to solve a mystery that involves both the wizarding and Muggle worlds.
One interesting plot could be that the wizards from Harry Potter world accidentally stumble upon the Shire while on a magical experiment gone wrong. They meet the hobbits and learn about their simple yet fulfilling lives. Meanwhile, the hobbits are in awe of the magic the wizards possess. Then, an ancient evil that threatens both the wizarding world and Middle - earth emerges, forcing them to combine their strengths. The wizards use their powerful spells and the hobbits' courage and resourcefulness to fight against it.
One idea could be that the magical world of Harry Potter has a security breach that the Incredibles are called to help with. Mr. Incredible could use his strength to move heavy magical objects or hold back magical creatures, while Elastigirl could reach into tight spaces in Hogwarts to retrieve lost magical items. Dash could be useful in quickly delivering important messages across the vast Hogwarts grounds. And Violet's force fields could protect students from dangerous spells.