A different plot could be that Iron Maiden is on a world tour when they accidentally stumble upon an alien technology that the Avengers are also after. This technology is the key to stopping an impending alien invasion. The two groups then have to work together, with Iron Maiden bringing their creative thinking and the Avengers their combat skills, to figure out how to use the technology and save the world.
Imagine if Iron Maiden was a secret organization in the Naruto world. They have their own unique set of abilities that are related to their music. Naruto is sent on a mission to infiltrate this organization. As he gets deeper into it, he discovers that their goals are not entirely evil, but they are at odds with the current power structure in the ninja world. This could lead to a complex story where Naruto has to decide whether to side with Iron Maiden or try to bring them into the fold of the existing ninja society.
A fanfiction idea could be that the members of Iron Maiden are secretly wizards from the Harry Potter world who have been living in the Muggle world all this time. They get called back to Hogwarts when a threat emerges that is connected to the Avengers' enemies. They use their music as spells and team up with the Avengers to fight the combined threat. For example, their guitar riffs could be like magic bolts that can stun enemies.
Well, a plot idea could be that in the fanfiction, the events of Iron Man 3 somehow get re - written in a way that Tony Stark's suits in that movie have a different origin. For example, they were actually created by an ancient civilization that he discovers accidentally, and this new knowledge ties into the Avengers' overall story arc. Also, we could have a story where the Extremis virus from Iron Man 3 spreads in a different way and starts to affect some of the other Avengers. This would force Iron Man to not only deal with his own problems related to the virus but also find a cure for his teammates. And then there's the idea of a parallel universe where Iron Man 3 never happened as we know it, but the Avengers are still dealing with the consequences of a similar threat, and they have to rely on Iron Man's knowledge from that 'alternate' Iron Man 3.
Perhaps in the fanfiction, the Avengers reunite for a more personal reason. One of their own, say Tony Stark (even if he's no longer alive in the main timeline), has somehow sent a distress signal from an alternate reality. They come together, not just to rescue him but also to explore this new and strange reality where things are different. They might meet alternate versions of themselves and have to team up with these versions to solve a problem that is affecting both realities.
One idea could be that the Avengers themselves get injured during a major battle and are taken to a special hospital. There, they have to deal with not only their physical wounds but also the psychological trauma. For example, Iron Man might struggle with the fear of his suit failing again while in recovery. The doctors and nurses in the hospital could be normal humans who are in awe of the Avengers but also have to keep their professional composure.
You can try fanfiction websites like Archive of Our Own (AO3). It has a vast collection of fanfictions from various fandoms, including those that combine Iron Maiden and the Avengers. Just use the search function and type in relevant keywords.
One way to combine them could be to create a multiverse - type story. Imagine Iron Maiden being a band that exists in both the Marvel Universe of the Avengers and the wizarding world of Harry Potter. The Avengers could be on a mission that somehow leads them to Hogwarts. Maybe they need to find a magical object that is hidden there to defeat a powerful enemy. And Iron Maiden's music could be the key to unlocking some hidden magic or power within the school. It would be a wild and creative crossover.
One possible plot could be that Oliver Queen gets transported to the Avengers' universe. He teams up with Hawkeye, sharing their archery skills and combat tactics. They could go on a mission to stop a new threat that combines the technology of the Arrowverse and the super - powered enemies of the Avengers.
One interesting plot could be Spider - Man having to prove himself to the Avengers. Maybe he starts as an outsider, but through his unique skills like web - slinging and his spider - sense, he helps the Avengers in a mission that they initially thought was impossible. For example, infiltrating a high - security enemy base that is full of high - tech traps.
A cool plot might be that the Tailed Beasts in the Naruto world are being targeted by an unknown force from the Marvel universe. The Avengers, thinking it could lead to a greater threat to both universes, come to help. Naruto and the Avengers have to work together to protect the Tailed Beasts. Hulk could have an interesting interaction with the Tailed Beasts, perhaps learning from them how to better control his rage, while the ninjas are amazed by Thor's lightning powers and try to incorporate some of that into their own jutsu.