A popular one is 'Potter in the DC Universe'. In this, Harry is sent to the DC universe due to a spell gone wrong. He has to adapt to a world without magic in the traditional sense but with super - heroes everywhere. It shows how his wizarding skills can still be useful in this new and different world.
There's 'Magic and Metahumans'. This fanfiction has a great plot where the Death Eaters from Harry Potter somehow end up in Metropolis. Superman has to deal with their dark magic while Harry and his friends try to find a way back to their world. It's full of action and interesting character dynamics.
There's 'Martian Magic: A Harry Potter - DC Crossover'. In this fanfiction, the Martian Manhunter discovers the wizarding world of Harry Potter. It's a great read as it shows how the Martian's unique abilities interact with the magic of Hogwarts. It also has some really cool team - up moments between the characters from both universes.
There's also 'Harry Potter in the DC Universe'. In this fanfiction, Harry finds himself somehow transported to the DC universe. He has to use his magic skills while also dealing with the superheroes and villains there. It's a really cool concept as it shows how his magic can be both an advantage and a source of confusion in a world full of super - powers.
Another interesting one is 'When the Bat Meets the Boy - Who - Lived'. In this fanfiction, Batman and Harry Potter cross paths. The story delves into how two very different heroes with their own moral codes and ways of doing things can work together or clash when faced with common threats.
There's also 'Potter's DC Adventure'. In this fanfiction, Harry finds himself in the DC world and gradually forms relationships with different characters. It's a great read if you like to see how the two different fictional universes blend together in the context of a harem story. The author does a good job of maintaining the essence of both the Harry Potter and DC worlds.
I also like 'Flash and Green Lantern: The Brave and the Bold'. This fanfiction has the Flash and Green Lantern teaming up in a way that showcases their unique powers. The plot takes them across different galaxies as they try to stop an intergalactic villain. It's full of humor, action, and great character development.
One popular one is 'The Akatsuki in Hogwarts'. It has an interesting plot where the members of Akatsuki find themselves in the wizarding world of Harry Potter. They bring their unique powers and personalities, which creates a lot of chaos and also some unexpected alliances. Another is 'Akatsuki's Magic Adventure at Hogwarts' which focuses more on how they adapt to the magical rules and customs in the school.
One popular 'harry potter sao crossover fanfiction' is 'A Wizard in Aincrad'. It combines the magical world of Harry Potter with the virtual reality of Sword Art Online in an interesting way. The characters from both universes interact in unexpected scenarios.
There's also 'Magic in the Rainy Town'. In this fanfic, Hermione finds herself in Forks for some reason and gets involved with the Cullens. It's really fascinating to see how her magic is perceived in the Twilight world and how she adapts to the new environment. The author does a great job of melding the two different settings and character traits.
One popular 'Harry Potter and Hetalia crossover fanfiction' is 'A Magical Meeting'. It combines the magic world of Harry Potter with the unique characters from Hetalia in a really interesting way. The story often has the Hetalia characters interacting with Hogwarts students and getting involved in magical adventures.
One great 'harry potter btvs crossover fanfiction' is 'The Slayer and the Boy Who Lived'. It combines the magical worlds of both Harry Potter and Buffy the Vampire Slayer in an exciting way, with Buffy finding herself in the wizarding world and having to team up with Harry to fight new threats.