One popular trope is the 'fish - out - of - water' story. For example, when Captain Marvel first arrives in the Harry Potter world, she's confused by all the magic. It's fun to see her adapt. Another is the 'team - up' trope, like Harry and his friends joining forces with Captain Marvel to take on a big bad. They combine their skills and powers.
The 'alternate universe' trope is also quite common. In some fanfics, there's an alternate reality where the two universes are merged. Captain Marvel might be a student at Hogwarts with magical powers on top of her superpowers. There's also the 'mentor' trope, where Captain Marvel mentors Harry or vice versa, sharing their knowledge and experiences.
The 'crossover romance' trope can be found too, although not as common. Some fanfictions might explore a romantic relationship between a character from Harry Potter and Captain Marvel. For instance, Hermione could develop feelings for Captain Marvel as they work together. However, this trope is more niche compared to the others.
A common trope is power - related. In Harry Potter and Marvel fanfiction, you often see characters either sharing or comparing their powers. For instance, how would Captain America's physical abilities stack up against a wizard's magical skills? Also, the 'found family' trope is there. Characters from both universes coming together to form a new family unit, like some Avengers joining forces with the Hogwarts crew.
In 20 years of Harry Potter fanfiction, there are several popular tropes. The 'Powerful!Harry' trope is quite common. Fans like to write about Harry having even more power than in the books. Also, the 'Soulmate' trope is popular, especially when it comes to romantic pairings. And the 'Dark!Hermione' trope has emerged, where Hermione takes a more morally ambiguous or even dark path, which is an interesting twist on her character.
The 'Power Transfer' trope is often seen. This is when a character from one series gains the power or ability from the other series. Say, Harry getting the ability to see ghosts like Sam does in Supernatural. And then there's the 'Shared Enemy' trope. A threat that is dangerous to both the wizarding world and the Supernatural world forces the characters to cooperate, creating exciting storylines.
A very common trope is the 'Dark!Harry' concept. In these stories, Harry turns to the dark side, either because of being mistreated or for some other reason. It's interesting to see how the story unfolds when the main hero becomes an anti - hero. Also, the 'Teacher - Student Romance' trope exists, though it's a bit controversial. But it does add an element of forbidden love to the stories.
One popular trope is the 'alternate universe' where the story takes place in a different setting or with different rules from the original series. For example, a wizarding world where Voldemort never existed. Another is the 'character redemption' trope, like Draco Malfoy getting a chance to be a good person from the start. And 'romantic pairings' that fans love to explore, such as Hermione with someone other than Ron.
One common trope is the 'fish out of water' situation where Castiel is suddenly in the Harry Potter world and has to figure out how things work. Another is the 'powerful ally' trope where he becomes a crucial help to Harry and his friends.
One common trope is the 'fish - out - of - water' situation. The fem Harry Potter character is suddenly in a very different world like Marvel, and she has to adapt. Another is the power - comparison trope, where her magic is compared to the superpowers in Marvel. For example, how her ability to apparate might be better or different from Quicksilver's speed.
The 'fish - out - - water' trope can be seen too. Maybe Captain Marvel is in a new part of the galaxy where Star - Lord is more familiar, or vice versa. It creates opportunities for humorous situations as they learn about each other's worlds and cultures. This trope can also lead to character growth as they adapt to new environments.
One popular trope is the 'Older Brother Figure'. Bill often takes on this role for Harry in fanfiction. For example, in many stories he gives Harry advice on dealing with Voldemort. Another is the 'Mysterious Curse - Breaker' trope. Since Bill is a curse - breaker, fics often play up the mystery and danger of his job. A third popular trope is 'Weasley Family Bonds'. Fanfictions explore how Bill's actions and decisions affect the whole Weasley family.
One popular trope is the 'new student at Hogwarts' where the main character, often an original creation, enters the school and has to navigate the complex social and magical world. Another is the 'discovering a hidden power' trope, like finding out they can communicate with magical creatures in a unique way. And of course, the 'romance between houses' trope, such as a Hufflepuff falling in love with a Ravenclaw, which adds an interesting dynamic to the story.