Perhaps there's a plot where She - Hulk is from an alternate dimension where the wizarding world and the world of superheroes co - exist. She comes to the main 'Harry Potter' dimension to seek help because her world is under threat. The Hogwarts professors and students have to work with her to find a way to save both their worlds, and along the way, there are a lot of cultural clashes and exchanges of knowledge between the two different universes.
There could also be a plotline where they both enter a mysterious tournament. They have to fight other superheroes and villains in a series of battles. Along the way, they learn more about each other's capabilities and form a stronger bond.
In a Naruto - Hulk fanfiction, a plotline could involve the Hulk being seen as a new form of tailed beast. The ninja would be unsure how to deal with him. Naruto, on the other hand, might see similarities between the Hulk and himself when he loses control of the Nine - Tails' power. He could try to help the Hulk gain control over his rage. Or perhaps a villain from the Hulk's world follows him to the Naruto world and they have to team up to defeat this new threat.
One idea could be that She - Hulk, in her human form, discovers she has magical abilities and gets a letter from Hogwarts. She then has to navigate the wizarding world while also dealing with her Hulk - like powers. It would be interesting to see how she interacts with the magical creatures and students at Hogwarts, like when she meets Hagrid or has a duel with Draco Malfoy.
One plotline could be Naruto being a transfer student at Hogwarts. He might struggle to adapt to the magic system while also showing off his ninja skills. Another could be Naruto teaming up with Harry Potter to fight a common enemy that threatens both the ninja world and the wizarding world.
One possible plotline could be that Harry, after some dark magic influence or a strange accident, starts to show Joker - like behavior at Hogwarts. He might play cruel pranks on his classmates and teachers, using his magic in unexpected and unethical ways.
One possible plotline is that Broly is brought to the Harry Potter world as a result of a powerful spell gone wrong. He initially causes chaos with his strength but then gradually learns about the concept of magic and starts to respect it. Another could be that Broly is a hidden protector of Hogwarts, his Saiyan powers being the ultimate defense against a new dark force that the normal magic in the wizarding world can't handle.
A possible plotline could be that Harry uses his invisibility to spy on Voldemort's followers and gather intelligence for the Order of the Phoenix. This would add an element of mystery and danger as he has to be extremely careful not to be detected.
Maybe Aragorn is summoned to Hogwarts by a powerful spell gone wrong. Once there, he has to figure out how to get back to Middle - earth while also getting involved in the magical world's problems. He could end up teaching the students about non - magical combat skills.
A possible plotline could be that lithium is a key ingredient in a new spell that a young wizard discovers. This spell could be used to combat the dark forces in a unique way. Another plotline might be that lithium is found in a hidden part of the Forbidden Forest and it has some sort of connection to an ancient magic that was long forgotten.
One possible plotline could be that Harry Potter and his friends are magically transported to the NBA world. They then use their magic to enhance their basketball skills and compete against the best players. Another could be that NBA players visit Hogwarts and learn about magic while also teaching the students about basketball.