If Peter Pan joined the Avengers, he would bring a sense of whimsy. He could use his ability to fly and small size to his advantage in battles. For example, he could fly into enemy strongholds unnoticed and gather intelligence.
Another idea is a crossover with The Chronicles of Narnia. Peter could enter Narnia through some magical portal. He'd interact with the talking animals and the Pevensie children, and his skills in fighting pirates could be useful in Narnia's battles.
One possible plot could be that Tinkerbell gets jealous when Peter Pan brings a new friend from another world to Neverland. She tries to play tricks on the new friend but accidentally endangers all of Neverland. Then she has to team up with the new friend to save Neverland and in the process, she and the new friend become closer, while Peter Pan learns a lesson about friendship and jealousy.
Begin by creating a unique scenario that brings the two stories together. Let's say for a Peter Pan and Lord of the Rings crossover. You could start with Peter being drawn to Middle - earth by the power of the One Ring. As you write, focus on how the different rules of magic in each world will affect the story. In Peter Pan's world, it's more about fairy - like magic, while in Middle - earth it's more about the power of the Elves and the Rings.
One idea could be that Peter Pan and his Lost Boys end up in a different Disney world, like the world of Beauty and the Beast. They might mistake the Beast for a new kind of pirate or monster at first. Another idea is that a Disney princess, say Cinderella, gets whisked away to Neverland by Peter Pan. She could teach the Lost Boys some manners while they teach her how to have more fun. Also, Tinker Bell could get jealous of a new Disney character who catches Peter Pan's attention, like Ariel from The Little Mermaid.
In many Disney Peter Pan fanfictions, Peter Pan does get hurt. Writers may do this to add depth to his character. When he gets hurt, it can lead to different reactions from the other characters in the story, like Wendy taking care of him. It also allows for a different kind of growth in the story. For example, he might become more cautious or learn a valuable lesson about his overconfidence. And it can also create new storylines where the characters have to find a way to heal him, which can be very interesting to read.
Captain Hook would initially feel victorious. But then he might realize that Peter was an important part of Neverland's balance. Without Peter, the eternal battle that gave his life purpose is gone. He could start to feel lost and even a bit regretful for all the times he tried to kill Peter.
Well, in such a crossover, Peter Pan could use his flying ability to outmaneuver the Avengers at first. Maybe he'd steal Captain America's shield just for fun. Then the Avengers would have to figure out how to deal with this mischievous boy who doesn't play by their rules. Iron Man could try to use his technology to track Peter, but Peter's magic might interfere with it.
One possible plot could be that Peter Pan takes Harry Potter and his friends to Neverland. There, they encounter the Lost Boys and Tinker Bell. Harry discovers new magic in Neverland that's different from Hogwarts magic. They could also face a common enemy, like a dark force that's trying to take over both Hogwarts and Neverland. The wizards could teach the Lost Boys some basic spells, and in return, the Lost Boys could show them how to fly better than on broomsticks.
One idea could be that Peter Pan takes Harry Potter to Neverland to escape from Voldemort. In Neverland, Harry discovers new magical abilities that are different from those in the wizarding world. He could learn to fly in a more carefree way like the Lost Boys and use his magic in new and exciting environments.