The plot could revolve around a power struggle. There could be a new power source or a special item that has emerged in the Smash Bros world. Different characters have different ideas about how to handle it. Some want to use it to gain more power and control, while others believe it should be destroyed or shared equally. This causes a split and a civil war breaks out. For instance, if there was a new power - up that could make a character invincible, characters like Bowser might want to hoard it, while Mario would want to share it among everyone.
The main characters would likely include Kirby. Kirby is known for his cute appearance but powerful abilities. He could be caught in the middle of the civil war or choose a side based on his own simple yet strong sense of right and wrong. Then there's Pikachu. Pikachu is extremely popular and his electric powers could be a great asset in the battles of the civil war. It could be siding with the group that wants to protect the Smash Bros world from chaos or be part of a group that wants to change the existing order.
One possible plot could be that Thanos somehow enters the Super Smash Bros universe. He could be after the Smash Bros' power sources or something equivalent to the Infinity Stones in their world. The heroes from various game franchises in Smash Bros would have to team up to stop him. For example, Mario and Link might work together to find a way to defeat Thanos' powerful attacks.
One interesting plot could be that Ash and Pikachu get transported into a strange, distorted version of the Super Smash Bros world. The rules are all mixed up, and they have to figure out how to win battles. They encounter some really odd versions of their old friends and foes. Pikachu has to learn new ways to use its attacks, and Ash has to come up with new strategies. Maybe they have to team up with some unlikely allies to get through the challenges. For example, they might have to work with a villainous Pokémon they once fought against. This would create a lot of interesting character dynamics and battles.
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.
Well, a really engaging plot point often involves Naruto bringing his unique ninja techniques into the Smash Bros arena. For instance, his ability to use chakra in a world full of characters with different power sources. Also, the idea of Naruto trying to understand the Smash Bros power - ups and how they can enhance his abilities or those of his newfound allies. And then there's the whole concept of Naruto facing off against characters with completely different moral compasses than his own, like some of the more villainous Smash Bros characters.
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.
A unique plot. For example, if it combines the different universes and characters from Super Smash Bros and Infinity War in a way that's unexpected. Maybe having characters from Super Smash Bros interact with the Infinity Stones in a creative manner.
Black Widow would rely on her agility and combat skills. She could have quick, multi - hit attacks like some of the faster characters in Smash Bros. Her special moves could include things like her Widow's Bite for a stun effect. Captain America, with his shield, could have a good balance of offense and defense. His shield throws could be ranged attacks, but he also needs to be vulnerable when he throws it, like in the actual Smash Bros. game where characters are exposed after certain attacks. This way, his power is not too overbearing.
Dark Samus can be a central figure in fanfiction. Her dark nature stands out among the Smash Bros cast. She might be used to introduce new challenges for the other characters. For instance, she could disrupt the normal Smash Bros tournaments in the fan - made stories.