Maybe Harry is recruited into a special magical army. His task could be to train other soldiers in defensive magic. And he has to deal with the challenges of military discipline while still being the famous Harry Potter. He could face a situation where he has to choose between following military orders and his own moral code when it comes to using magic in combat.
In this fanfiction, Harry could be a soldier in a war between different magical kingdoms. He would be using his Patronus not just for protection against Dementors but as a signal or a weapon in battle. He might also have to learn new forms of magic that are more combat - effective, like creating magical shields that can withstand powerful attacks from enemy wizards. And there could be a lot of political intrigue involved as well, with Harry having to navigate the complex relationships between different military leaders in the magical world.
Perhaps in the fanfiction, Ron could shift into a magical creature like a hippogriff. This would give him new abilities such as flying and enhanced strength. Also, Dumbledore could be reimagined as a shifter who can shift into a phoenix - like form, which would add a new layer to his already mysterious character.
Maybe Naruto meets a group of friendly ghosts who teach him some unique jutsu that are related to the spirit world. Or perhaps there is a powerful ghost that has been sealed away for a long time, and Naruto accidentally releases it. Now he has to team up with his friends to reseal the ghost before it causes chaos in the ninja world. It could also be that Naruto's spirit is separated from his body and he has to navigate the spirit realm, which is full of other ghosts, to get back to his body.
One way could be that the dialogue of some characters is in one language, say English, while the descriptions or internal thoughts are in another language like German. For example, Harry might be speaking English when interacting with his friends, but when we get a peek into his deeper thoughts about his past or his feelings towards Voldemort, it could be in German.
In this kind of fanfiction, we could see Ron being able to use psychometric magic to understand the history of the Weasley family heirlooms. Maybe he touches an old broomstick and gets visions of all the Weasley siblings who have used it before. Also, Dumbledore could have known about a psychometric spell and used it to study the history of Hogwarts itself, finding out secrets about the founders by touching objects they left behind.
One example could be a fanfiction where Harry uses his invisibility cloak in a more devious way to play pranks on the Slytherins, rather than just for sneaking around. Another might be if Ron uses his chess skills not just for playing the game but to outwit his enemies in a more strategic and underhanded way.
One example could be in a fanfic where Ron makes a joke at Hermione's expense during a big wizarding event. Hermione, who has been dealing with his teasing for a while, finally snaps and gives him a piece of her mind in front of everyone.
Sure. There could be fanfictions where the author completely misinterprets the relationships between characters. For instance, making Harry and Draco best friends from the start without any of the rivalry and tension that was built in the original series. Then there are those that have really bad pacing. They might spend too much time on unimportant details in the beginning and then rush through the important parts of the story like the climax. And sometimes, the worst ones have a very unoriginal plot. It's just a rehash of the original books but with some minor, uninteresting changes.
One way could be that Harry is wrongly accused of using dark magic. As a result, the wizarding world turns against him and he becomes an outcast. He then has to prove his innocence while dealing with the hatred and fear of others.
He could be creating a dedicated folder on his computer for all his favorite fanfiction stories, which is a simple way of 'nesting'.
Maybe Harry is unable to perform basic spells because he's so coddled that he hasn't had the chance to practice properly. So, his friends have to constantly protect him from minor threats like a pesky pixie.