One interesting storyline could be that Spider - Man gets transported to Elsa's world. He could use his web - slinging skills to traverse the icy landscapes. Maybe he helps Elsa control her powers better by showing her how to be more precise with her abilities, like he is with his webs.
One interesting storyline could be about Spider Man facing a new villain that was created specifically for the fanfiction. This villain might have powers that directly oppose Spider Man's, like the ability to nullify his spider - sense.
One interesting storyline could be Spider - Man and Falcon teaming up to stop a new supervillain in the city. This villain might have powers that require both of their unique skills to combat. For example, the villain could be able to fly and shoot energy blasts, so Falcon can take to the air to engage in aerial combat while Spider - Man uses his agility to dodge the blasts on the ground and find a way to disable the villain's power source.
One interesting storyline could be Spider Man and Firestar teaming up to take on a new supervillain in their city. This villain could have powers that force them to use their combined skills in unique ways, like Firestar's ability to fly and create heat blasts along with Spider Man's agility and web - slinging.
One interesting storyline could be Spider Man and Valkyrie teaming up to fight a powerful new villain in New York. Valkyrie's Asgardian powers combined with Spider Man's agility and web - slinging would make for an epic battle. Maybe the villain is a powerful sorcerer who is trying to open a portal to a dark dimension and they have to stop him before it's too late.
One interesting storyline could be Spider - Man and Tigra teaming up to fight a new super - villain in the city. Maybe a villain who can control the minds of animals, and Tigra's connection to her feline side makes her both a target and an important asset in the fight. Another could be a story where Spider - Man has to help Tigra when she gets caught in a scientific experiment gone wrong that starts to change her powers in unexpected ways.
One interesting storyline could be Spider - Man having to use his unique abilities to solve a mystery within the Avengers' headquarters. His agility and spider - sense might lead him to discover a hidden threat that the other Avengers overlooked.
In some fanfictions, Spider - Man's mother might be from an alien race. This would bring in elements of science - fiction and could explain some of his unique powers in a different way. For example, his ability to climb walls could be related to some alien genetic trait. Also, it could lead to a plot where he has to deal with his alien heritage and the implications it has on his life as a superhero.
One interesting storyline could be Ghost Rider and Spider - Man teaming up to take on a powerful demon that has escaped from the underworld and is causing chaos in New York. Spider - Man's agility and intelligence combined with Ghost Rider's hellish powers would make for an epic battle.
A third storyline might be that there's a misunderstanding between Spider - Man and Deadpool. Deadpool is hired to do a job that Spider - Man thinks is wrong. So, they start off as enemies in the fanfiction. But as they fight and exchange banter, they realize they've been set up by a bigger bad guy and end up working together to take this real villain down.
One interesting storyline could be Peter and Harry teaming up against a new villain in the city. They combine their skills and resources to take on this threat that neither could handle alone.