Perhaps Spider - Man has to enter a dimension of pure shadow in the fanfiction. In this dimension, his powers work differently, and he has to learn new ways to fight and survive while also trying to find a way back to his own world.
One idea could be that Spider - Man discovers a new shadow - based villain who can manipulate the darkness in ways he's never seen before. The villain could be creating shadow creatures to terrorize the city at night.
One idea could be a crossover with the X - Men. Spider - Man could find himself in a situation where he has to team up with the mutants to fight a common enemy that is using the symbiote technology from 'Web of Shadows' against both groups. Another plot could involve a crossover with the Fantastic Four. Maybe the symbiote invasion in Spider - Man's world starts affecting the Negative Zone, and they have to work together to stop it from spreading further.
One idea could be exploring what would happen if Spider - Man had to team up with his villains to fight a greater threat from another dimension. For example, Venom and Green Goblin might be forced to work with him.
A plot could be that Black Cat gets infected by a different kind of symbiote that gives her new powers. She has to learn to control these powers while also dealing with the fact that Spider - Man is a bit suspicious of her new abilities.
One idea could be exploring the different Spider - People's home universes in more detail. For example, showing what Miles Morales' daily life in his universe was like before becoming Spider - Man. Another could be a team - up between Miles and an older, more experienced Spider - Person from a different universe to face a new and powerful villain.
Perhaps there's a fanfiction where Spider Man and Spider Gwen accidentally swap powers. They have to learn how to use each other's abilities to fight crime. This would lead to some really funny and also challenging situations as they get used to different ways of web - slinging and sensing danger.
One plot idea could be that Spider Man and Spider Woman team up to fight a new supervillain who has the power to manipulate time. They have to figure out how to work together while also dealing with the chaos the villain is causing in different timelines. Another could be a story where they get trapped in an alternate dimension and have to find a way back home while facing strange new enemies. Maybe there's a plot where they start to have feelings for each other but are afraid it will interfere with their superhero duties.
Maybe in the fanfiction, Spider - Gwen gets lost in the future where Spider - Man 2099 exists. He has to help her get back to her own time while also protecting his own version of New York from the chaos her presence might bring. They could learn from each other's fighting styles and develop a unique bond in the process.
Perhaps in a fanfiction, the Raft is under a siege by an unknown force. Spider - Man, despite being a prisoner, decides to help defend it. He teams up with some of the more morally ambiguous inmates. Together, they have to overcome their differences and fight off the attackers while also dealing with the internal power struggles and security issues within the Raft.
One idea could be exploring the relationship between Spider - Man 2099 and other superheroes in the future. Maybe he teams up with a new group of heroes to fight a powerful villain who threatens the entire city.
One plot idea could be Spider Man having to face a powerful new villain all by himself in a post - apocalyptic New York. The city is in ruins, and he has no backup from the Avengers or other heroes. He has to rely on his wits and his web - slinging skills more than ever.