One interesting story could be about a hidden magical society within the underground of Hogwarts. They might have their own set of rules and magic that is different from what is taught above ground. For example, they could be using a more ancient form of magic that has been forgotten by most wizards on the surface.
One characteristic is the creative use of magic in battles. Writers often come up with new spells or unique ways to use existing ones. For example, in some fanfictions, a character might combine two spells to create a more powerful effect during a fight.
In fanfiction, 'Harry Potter Master of Fighting' could be a concept where Harry Potter is depicted as having extraordinary combat skills. Maybe the author wants to explore a different side of Harry, one that is more focused on physical and magical combat mastery compared to the original story.
He might encounter some strange magical creatures that are only found underground. For example, there could be a new type of goblin or a magical mole with special powers.
You can start by looking at fanfiction websites like FanFiction.net or Archive of Our Own. Use the search function and type in 'Harry Potter underground' to get relevant results. Check the ratings and reviews of the stories to see if they are worth reading.
Some fanfiction writers may have a different vision for Harry Potter's character. They might see him as more of a diplomat or a healer within the wizarding world, rather than a fighter. So, they write stories that reflect this different view of the character, where he uses his wits and other skills rather than engaging in physical or magical combat.
Well, consider a scenario where Sonic and his siblings are mistaken for some new kind of magical beings at Hogwarts. The students are curious and a bit scared at first. Ron might make some clumsy attempts to befriend them, which could lead to some comical situations. Meanwhile, Sonic's speed could come in handy during a dangerous situation at Hogwarts, like when a group of Death Eaters attack. And Sonic's siblings could use their music to calm the panicked students and staff, showing a new side of their powers to the Harry Potter characters.
One idea could be that Sonic and his siblings get transported into the Harry Potter universe. They could use their speed and musical powers to help Harry and his friends in their battles against Voldemort. For example, Sonic could quickly deliver important messages or objects across Hogwarts while his siblings use their music to soothe or even temporarily stun the dark creatures.
There's a chance he'll meet other outcast wizards. These wizards might have been shunned by the wizarding world above ground. They could be very different from the wizards Harry is familiar with, perhaps having their own unique styles of magic. They might initially be hostile to Harry, seeing him as an outsider from the 'normal' wizarding world, but later they could become his allies. They might also know secrets about the underground world that could help Harry in his future battles or quests.
Perhaps it implies that the essence of Harry Potter's story in the canonical works is complete, and there's no need for more fictional fighting scenarios as seen in fanfiction. The official narrative has run its course, and fanfiction's fighting - related ideas are now redundant.