One main theme is usually the clash of different fighting styles. Naruto has his ninja skills and the Smash Bros. characters have their own unique moves. Another theme could be friendship, as Naruto might form bonds with other characters in the brawl.
I'm not sure specifically which one is the longest 'Super Smash Bros. Brawl' fanfic. There are likely many fanfics out there, and it would require a lot of research in the various fanfic platforms to determine the absolute longest one. It could be a complex, multi - chapter epic that delves deep into the game's characters, their relationships, and the battles in the Smash Bros. universe.
Another theme is the pursuit of power. Characters are always looking to improve their skills and become stronger in the game. Fan fictions can expand on this, like a character going on a special training journey to master a new move or gain an edge in the brawl.
There are quite a few 'naruto super smash bros brawl fanfic' out there. For example, 'Naruto in the Brawl World'. In this fanfic, Naruto is summoned into the Smash Bros. brawl world by some mysterious force. He quickly realizes that he needs to master new combat techniques to compete. The fanfic details his journey of learning about the Smash Bros. mechanics while still relying on his ninja abilities. It also has some great character interactions between Naruto and the Smash Bros. regulars, making it a fun read for fans of both Naruto and Super Smash Bros.
One idea could be a story where all the characters from different universes in Super Smash Bros Brawl team up to fight a new, powerful and unknown threat that is disrupting the balance of their world. For example, a strange dark energy is starting to corrupt the stages and they have to find the source and stop it.
Well, first off, check out the big fanfic platforms. FanFiction.net is a classic place to start. They have a search function that allows you to narrow down to 'Super Smash Bros. Brawl' fanfics. Once you've got the list, you can scan through and look for ones that seem really long. Archive of Our Own is also great. It has a more modern interface and a community that's really into detailed fan works. You might also want to check out some Smash Bros. - specific forums where fans might discuss and share long fanfics.
Give them unique personalities. For example, if you have Mario in your fanfic, don't just make him the typical hero. Maybe he has a fear of heights which he has to overcome during battles on high - altitude stages. This adds a new dimension to his character.
One idea could be a story where all the characters from different universes team up to face a new, unknown threat that is causing glitches in their worlds. For example, Mario, Link, and Pikachu working together in a way they never have before.
Mario is often a popular choice. He's such an iconic character that people love to write about his adventures in the Smash Bros world. His relationship with other characters, like Luigi or Peach, can be explored in many ways.
An interesting plot for a Super Smash Bros Brawl OC fanfiction could involve an OC that is a master of disguise. This OC can transform into any of the existing Smash Bros characters, but with a twist. Their abilities are a bit different from the original characters. They use this power to create chaos during battles, making other characters suspect each other. As the story progresses, they start to have a change of heart and end up using their power for good, helping the Smash Bros community deal with an outside threat that none of the regular characters can handle alone.
To create a unique OC for Super Smash Bros Brawl fanfiction, consider their appearance. Make it distinct from the existing characters. Maybe they have a robotic body with living plants growing out of it if you want to combine nature and technology. Their personality is also crucial. Are they a cocky fighter who taunts a lot, or a more reserved and strategic one? Their backstory should tie into their personality and abilities. If they have a tragic past, it might explain why they fight so aggressively or defensively. And don't forget about their fighting style. It should be something that stands out, like a character who fights using only their feet or a character who uses psychic powers to control the stage elements.