Maybe in the fanfiction, the Avengers are having trouble with a villain who has the ability to create illusions. Spiderman's spider - sense helps him see through the illusions and he joins the Avengers to defeat the villain. He also teaches the Avengers some of his acrobatic fighting moves along the way.
Another plot could be that Spiderman is accidentally transported to an alternate dimension where he meets a different version of the Avengers. They initially don't trust him but as they face a common enemy, they learn to work together and Spiderman eventually finds a way back to his own dimension.
One idea could be that Spiderman discovers a new threat in his neighborhood which turns out to be linked to a much larger plot involving the Avengers. So he has to convince the Avengers to take him seriously and work together to stop it.
One plot idea could be that the Avengers discover Spiderman's identity during a mission when his mask gets damaged. Then they have to protect his secret from villains who are also after it.
Well, a cool plot could involve Spider - Man's identity being revealed to the public and the Avengers having to protect him from various villains who see this as an opportunity to take him out. Or perhaps a situation where an old enemy of the Avengers teams up with one of Spider - Man's foes, forcing the two groups to work together more closely than ever. Spider - Man could also introduce some new tech or fighting styles to the Avengers during their joint adventures.
One idea could be Deadpool trying to join the Avengers but constantly annoying them with his non - stop chatter and crazy antics. For example, he could keep interrupting their strategy meetings with his own hare - brained plans.
One idea could be a battle where the Eternals and Avengers are initially at odds due to a misunderstanding. Maybe they both think the other group is causing some strange cosmic events. Eventually, they figure out it's a third party and team up.
One idea could be that the Avengers need the Agents of Shield's help to track down a new, powerful and elusive villain who has technology that can disrupt the Avengers' powers. The Agents use their espionage skills to gather intel while the Avengers provide the muscle when it comes to confronting the bad guy.
A possible plot could be that the meeting causes some sort of time rift. The Avengers then have to fix this rift while also dealing with the differences between their present and past selves. Their past selves might be more naive or idealistic in some ways, which could lead to both comical and tense situations.
One plot idea could be that the Avengers find Stan Lee's old unpublished comic scripts during an adventure. They then use the ideas in the scripts to defeat a new, powerful villain who is immune to their usual tactics. Another could be that Stan Lee, as a spirit, visits the Avengers to give them moral support and some secret wisdom before a big battle.
A great plot could be that a member of the Avengers gets lost in space and is found by the Guardians. The Guardians then have to bring this Avenger back to Earth, but on the way, they encounter a series of challenges that require the combined skills of both groups. Along the way, they form strong bonds and exchange knowledge about their respective worlds.
A plot could involve Spiderman accidentally getting caught in an Avengers - level battle right in his neighborhood. He then has to prove himself to the Avengers while also protecting his home and friends. Maybe he discovers a connection between the villain in the battle and the local crime in his area that he's been trying to stop in 'Homecoming'.
One idea could be that the Avengers are accidentally transported to a movie set where the cast is filming their story. They initially think it's some kind of new villain's trick. Another could be that the cast members get to experience the powers of the Avengers for a day through a magical mishap.