You could write a fanfic about the backstories of how the characters got invited to the Smash Bros tournament. Maybe there's some sort of secret council that decides who gets to participate, and there are some political intrigues among the different game worlds regarding this. So, like, Sonic's world is trying to get more representation in the tournament, but there are some forces that are against it.
One idea could be a crossover with a classic RPG like Final Fantasy. Characters from Final Fantasy could enter the Super Smash Bros universe and bring their unique abilities. For example, Cloud could use his Omnislash. Another idea is a crossover with an anime like Naruto. Naruto characters would add a whole new dynamic with their ninja skills. And a third idea could be a crossover with a horror game, like Resident Evil. The spooky elements and unique weapons of Resident Evil characters would make for a very different kind of Super Smash Bros fanfic.
A Smash Bros fanfic could focus on the backstory of a less - known character. For example, tell the story of how Mr. Game & Watch came to be in the Smash Bros universe. Explore his origin, his first battles, and how he got discovered to be part of the roster.
Well, you could have a story where a new villain emerges in the combined Naruto - Super Smash Bros world. This villain has the power to steal the abilities of the characters. Naruto and his comrades, along with the Smash Bros characters, have to team up to stop this villain. They go on a journey across different stages of the Smash Bros game to find the source of the villain's power and defeat him. Along the way, there are many battles, character development, and some humorous moments as the two different groups of characters interact.
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.
A plot could revolve around a new character being added to the roster secretly. This character has an unknown power that starts to disrupt the balance in the Smash Bros world, and the other characters must figure out who it is and stop them. For example, this new character could be causing glitches in the battle arenas, making it difficult for the regular characters to fight.
One idea could be a tournament arc where Naruto characters enter the Smash Bros universe and compete against the regular Smash Bros characters. They have to adapt to the different fighting styles and arenas.
The creativity in world - building is also notable. Fanfic writers can create their own versions of the Smash Bros universe, adding new locations or rules. It might include places inspired by the different stages in the game but with a new twist, like a haunted version of a familiar stage.
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.
One idea could be an OC from a relatively unknown game getting invited to the Smash Bros universe. They have to learn the ropes of the unique fighting style there. Another could be an OC who has a special power that disrupts the balance in the Smash Bros world, causing both chaos and new alliances among the characters.
One interesting plot idea could be a character who is new to the Smash Bros universe and their reaction to meeting all the iconic characters. They could start off in awe, gradually learn the ropes of the battles, and form unexpected friendships or rivalries. For example, a character from a relatively unknown game enters and is initially intimidated by Mario and Link but then discovers they have unique skills that can hold their own. Another plot could revolve around a character's reaction to the constantly changing stages, like being really confused when suddenly transported to a new and wacky stage.