A great way to combine them is through a magical experiment gone wrong. Maybe a wizard in Hogwarts was trying to create a new type of magical creature and accidentally summoned Pikachu. Then, Pikachu starts to interact with the students, like helping Hermione with her studies by using its electric shocks to represent different spells, which could be a really interesting and fun combination.
Imagine that Pikachu is the key to unlocking a hidden magical power within Harry. The two meet in a mysterious forest near Hogwarts. Pikachu's presence somehow awakens a dormant power in Harry that is related to electricity, and together they have to figure out how to control this new power to defeat Voldemort. This would involve a lot of character development for Harry as he adjusts to this new aspect of his magic.
A way to combine them could be through a shared enemy. Let's say there's a new dark force that is affecting both Sonic's world (where Shadow is from) and the wizarding world. Shadow and Harry, along with their respective friends, have to work together to defeat this enemy. They would have to learn to communicate despite their different backgrounds and abilities. Shadow might teach the wizards some physical combat skills, while the wizards could teach Shadow about magic. This kind of interaction between the two groups of characters would make for an exciting fanfiction.
Edward's alchemy skills and Harry's magic could combine in combat. For instance, Edward could transmute the environment to create barriers or platforms, while Harry uses spells to attack over or through these structures. Hermione's knowledge of magic and Edward's knowledge of alchemy could lead to some amazing new discoveries. They could combine their research skills to find solutions to problems that neither world has faced before.
The Avengers' superpowers and the magic of Harry Potter characters can combine in many ways. For instance, Captain America's combat skills combined with Harry's ability to use spells like Expelliarmus could make them a formidable duo in a fight. They could teach each other new fighting techniques.
Well, in fanfiction, you could have Harry's magic interact with the Incredibles' superpowers in a fight. For instance, if they were facing a common enemy. Harry could use spells to enhance the Incredibles' powers. His levitation charm on Mr. Incredible could make him jump even higher and land more powerfully.
It can combine the two by having the characters cross over. For instance, Harry could be invited to MI6 to share his knowledge of dark magic as they face some sort of dark magical threat in the Muggle world.
Iron Man's technology could be combined with the magic of the wizarding world. For example, he could use his repulsor rays along with a magic amplification spell. Harry Potter's ability to use the Patronus charm could be used in tandem with Captain America's leadership skills to inspire the combined group in a battle.
Imagine if the Geass power could be used to control magical creatures in the Harry Potter world. Lelouch could use his Geass on a Hippogriff or a dragon to do his bidding. At the same time, wizards and witches could use their magic to enhance the Geass. For example, a spell could be cast on a Geass user to make their power last longer or be more powerful. And the Hogwarts houses could each have a different approach to using the combined abilities. Gryffindors might be more bold in using the new powers, while Ravenclaws would be more strategic and Hufflepuffs more ethical in their use.
They could be in a time - travel scenario. Harry Potter accidentally takes Rose and Dobby back in time. They have to work together to get back to their own time. Dobby's house - elf magic might be crucial in finding a way back, while Rose uses her modern - day knowledge of magic (maybe she's read a lot about old magic) to help them along, and Harry Potter uses his experience from his own adventures.
They can combine in terms of magic systems. In some fanfictions, the powerful and often incomprehensible magic in the Cthulhu universe might blend with the more structured magic of Harry Potter. For example, a spell in Harry Potter might be corrupted by Cthulhu's influence and become a more dangerous and unpredictable force.
Their powers could combine in a really cool way. Harry's magic could enhance Starfire's energy blasts. For example, he could cast a spell on her hands that would make her energy blasts more powerful or more accurate. On the other hand, Starfire's superhuman strength could help Harry in physical combat situations. If they were surrounded by enemies, Starfire could use her strength to clear a path while Harry used his magic to hold off any attackers from a distance.