In an 'ultimate spider man crossover fanfic', a really interesting crossover could be with Venom. But instead of being enemies, they team up. Maybe there's a new symbiote - like threat that is even more powerful and they have to combine their powers to defeat it. Another idea is a crossover with the Guardians of the Galaxy. Spider - Man gets accidentally transported into space and has to team up with Star - Lord and the gang to get back home while also fighting off some space - pirates.
One idea could be a crossover with the X - Men. Spider - Man could find himself in the middle of a conflict between mutants and anti - mutant forces. He'd have to use his quick thinking and agility to help the X - Men protect the young mutants. Another could be a crossover with the Fantastic Four. Maybe Spider - Man gets caught in one of Reed Richards' experiments gone wrong and they all have to work together to fix it while also dealing with a new super - villain that emerges from the chaos.
One idea could be Spider - Man teaming up with a new, original superhero created just for the fanfic. They could face a villain who has the power to manipulate time, causing chaos in New York. Another could be exploring what would happen if Spider - Man lost his powers temporarily and had to rely on his wits and the help of his friends to stop a crime wave.
Another plot idea is that the OC is a scientist who accidentally creates a new type of symbiote. This symbiote has different properties compared to Venom and Carnage. Spider - Man has to team up with the OC to control and understand this new creation, leading to a lot of action and character development.
Maybe there's a plot where an ancient artifact is discovered in the city. This artifact has a connection to White Tiger's heritage. Spider - Man and White Tiger must protect the artifact from a group of thieves who want to use its power for evil. As they guard it, they learn more about each other's pasts and grow closer as friends and allies.
One interesting plot idea could be Spider - Man teaming up with unexpected heroes from other universes. For example, he might work with a magical hero to fight a villain who has the ability to manipulate time. This would create a really cool dynamic as they combine their different skills and powers.
One idea could be creating an OC with a unique power set related to sound, like being able to manipulate sound waves for various effects such as creating sonic blasts or using echolocation. Another could be an OC who is a foreign exchange student from a technologically advanced country and brings in new gadgets to help Spider - Man. Maybe an OC who has a power to heal others but at a cost to their own health.
One idea could be that Spider - Man gets accidentally transported to the DC universe. He teams up with Batman to take on a common enemy like the Joker who has somehow gotten his hands on some Oscorp tech. They combine their detective skills and combat abilities to stop the chaos.
One idea could be that Spider - Man gets accidentally transported to the DC universe. He teams up with Batman to take on a new villain that is a combination of their rogues' galleries. For example, a villain who has the powers of Electro and can also control minds like Brainiac.
One idea could be that Spider Girl has to face a new villain who has the power to manipulate time. This would put her in situations where she has to correct the changes made to the timeline. Another could be a story where she teams up with other superheroes from different dimensions to fight a common threat that endangers all of the multiverse.
One idea could be a gender - bended Spider - Man facing different social expectations. For example, in the regular story, Peter Parker has his own set of challenges as a male superhero, but a female version might have to deal with things like being underestimated in a male - dominated superhero world. She could also have different relationships with the other characters. Maybe her friendship with Harry Osborn or her interactions with Aunt May would be more nuanced due to her being female.