Maybe Thanos somehow discovers the wizarding world and decides he wants to add the power of magic to his collection of Infinity Stones. He could be the main villain, and Harry, with his understanding of both magic and his new Avengers - like abilities, would have to lead the fight against Thanos to protect both worlds.
Well, perhaps Harry discovers the Avengers through some magical means like a spell gone wrong that transports him to the MCU world. He could be in awe of their powers and decide to learn from them, and then try to incorporate their fighting styles into his own magical battles.
Well, he'd probably bring his magic skills to the Avengers. He could use spells like Expelliarmus to disarm villains quickly. His broomstick flying skills might also come in handy for getting around in a hurry or for some unique battle maneuvers.
It could be a super - powered villain who has a vendetta against the Avengers. Maybe he sees Peter as a new and vulnerable target since he's just joining the team. This villain might have some connection to Peter's past that makes him especially interested in causing trouble for Peter and by extension, the Avengers.
Well, if Percy Jackson were to become an Avenger in fanfiction, there would be some interesting dynamics. For one, his loyalty to his demigod friends might conflict with the Avengers' way of doing things at times. But his ability to think on his feet, which he developed from all his quests, would help him adapt quickly. And his relationship with the other Avengers, like maybe a friendly rivalry with Thor over who has better control over elemental powers, could be a great plot point.
Well, it could be that Peter starts off as a regular guy who is just a huge fan of the Avengers. Maybe he follows all their news, collects their merchandise. One day, he gets a chance to meet them somehow, like through a Stark Industries internship. Then he gradually proves himself useful to them and they start to train him. Eventually, he becomes part of the team, with his own unique skills like his spider - powers adding to the Avengers' strength.
She might bring her unique skills. For example, her hacking abilities could be very useful for the Avengers in gathering intelligence. Maybe she would also form a special bond with some of the existing Avengers, like Natasha Romanoff. They could train together and share their combat experiences.
If Loki becomes an Avenger in fanfiction, it would be a wild ride. He'd bring his complex personality to the team. His relationship with Thor would also be an interesting aspect. They could have brotherly moments within the team dynamic. Loki might also start to develop real friendships with the other Avengers, which would be a big change for him.
Well, he could bring his unique water - controlling abilities to the Avengers. Maybe he'd be the one to put out the fires during big battles in the city. He might also form an interesting friendship with Thor, since they both have some connection to powerful elements.
In many fanfictions, Harry might have gained unique powers or skills that caught the Avengers' attention, leading to his inclusion.
Yes, there are quite a few out there. Some focus on Harry's unique abilities being transferred into the Death Avenger universe, creating really interesting crossovers. For example, there are fanfics where Harry uses his magic in unexpected ways within the Death Avenger setting.