A cool concept could be that Peter Parker is actually a wizard in the Harry Potter universe who was orphaned and sent to live with the Muggles. He discovers his wizarding heritage later and has to balance his life as Spider - Man in New York with his newfound magical abilities at Hogwarts. He could use his web - shooters and spells in creative ways to fight off villains that threaten both the Muggle and wizarding worlds.
In a Harry Potter and Spider - Man crossover fanfiction, perhaps the Venom symbiote attaches itself to a Hogwarts student. Spider - Man then has to travel to the wizarding world to stop the now - corrupted student from causing chaos. Along the way, he discovers that the magic in the wizarding world can both help and hinder his attempts to subdue the symbiote - controlled student. Harry and his friends might initially be suspicious of Spider - Man but then realize they need his unique skills.
Well, perhaps there's a giant spider that was once a wizard who was cursed. This spider could remember some of its former magical knowledge. Harry Potter stumbles upon it during one of his adventures in the Forbidden Forest. The spider offers to help Harry in his fight against the dark forces, in exchange for Harry trying to find a way to break the curse. Harry then has to figure out how to work with a spider - creature while also dealing with the prejudices of his friends who are scared of spiders.
One idea could be that Spider - Man finds himself magically transported to the wizarding world of Harry Potter. He could use his web - slinging skills in Hogwarts, perhaps to help catch the Golden Snitch during a Quidditch match in a very unorthodox way. The Hogwarts students would be both amazed and a bit confused by this strange new hero in their midst.
Maybe the Venom symbiote could find its way into the Harry Potter universe and attach itself to a wizard. This wizard would then have to struggle with the dark and aggressive nature of the symbiote while also dealing with the magical world's rules and expectations. Harry Potter and his friends would have to figure out how to separate the wizard from the symbiote without using traditional Muggle technology.
A possible way for a crossover to work is through a shared villain. Let's say a powerful dark wizard somehow gets hold of some Stark Industries tech and combines it with dark magic. This new threat catches the attention of both Spider - Man and Harry Potter. Spider - Man would bring his scientific knowledge and superhero skills, while Harry and his friends would contribute their knowledge of magic. They would have to learn to work together, with Spider - Man having to adapt to the strange rules of the wizarding world, like not being able to use his phone or other Muggle technology in Hogwarts.
There could be a situation where a Transformer's technology gets mixed with Oscorp's experiments. This creates a new kind of threat that Spider - Man has to face. The Transformers get involved because it's their technology that's been misused. Together, they figure out a way to reverse the effects and defeat the new hybrid - like villains.
One idea could be a crossover with the X - Men. Spider - Man could team up with Wolverine. Their different fighting styles would make for some amazing action scenes. Wolverine's brute strength and healing factor combined with Spider - Man's agility and web - slinging abilities would be a great combination.
One idea could be that during a mission crossover, Spider - Man gets injured while trying to protect a civilian from an unexpected attack by a powerful enemy. Maybe he takes a hit meant for an Avenger and his suit's technology malfunctions, leaving him vulnerable.
One idea could be that Tinkerbell finds her way into the wizarding world of Harry Potter. Maybe she gets accidentally transported there by some magical mishap. She could use her fairy magic in Hogwarts, like helping to repair broken objects in a more sparkly and unique way compared to the Reparo charm.
Another possibility is a scenario where Voldemort decides to expand his reach into the non - magical world and Batman becomes aware of this threat. He would then enter Hogwarts undercover to learn about magic and form an alliance with the Order of the Phoenix. The contrast between Batman's brooding, non - magical detective nature and the magical world would make for an interesting story.
One idea could be that Loki, being the mischievous character he is, finds his way into the wizarding world of Harry Potter. He could start causing chaos in Hogwarts, perhaps by disguising himself as a student or a professor and playing pranks that are far more elaborate than those of the Weasley twins. For example, he might turn the entire Great Hall into an ice rink during breakfast time.