Well, perhaps in the fanfic, the Avengers meet the cast during a Comic - Con event. But instead of a normal meeting, some villains attack the event and the Avengers and the cast have to team up to fight them. It would be a really cool mix of the real - world and the superhero world.
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.
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 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 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 exploring what if Loki had an unexpected ally within the Avengers. Maybe a character who was initially on the heroes' side but got swayed by Loki's charm or promises.
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.
One plot idea could be that the Avengers find Stan Lee's old unpublished comic scripts during an adventure.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.
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 Inhumans' city of Attilan is in danger and the Avengers are called in to help. The Inhumans are initially hesitant to accept their aid due to their differences, but they soon realize they need to work together. Another idea is a young Inhuman with a powerful but uncontrollable ability is found by the Avengers. They try to help the Inhuman learn to control it while also protecting them from those who would use their power for evil.
One idea could be an imagine where a new superhero joins the Avengers. They have a unique power that the team initially struggles to understand but eventually learns to utilize effectively. For example, a hero with the power to manipulate time on a small scale, like being able to slow down time for a few seconds during a battle.