Maybe a story where they team up with some of the more heroic characters in the Undertale world to face a common enemy. It would be interesting to see how their personalities clash and blend during the cooperation. For example, they might initially have different approaches to fighting the enemy, but gradually learn from each other.
One idea could be that the Terrible Trio targets Gotham's new high - tech research facilities. They plan to steal advanced technology to enhance their own criminal operations. Another plot could involve the Trio teaming up with a new, mysterious villain who has a vendetta against Batman and using their combined skills to try and finally defeat him. A third plot might be that the Trio discovers Batman's secret identity and tries to use it to blackmail him into leaving Gotham.
One idea could be exploring the origin of the Creation Trio's powers. Maybe they got their powers from an ancient and mysterious Pokemon or a powerful energy source in the Pokemon world. Another idea is to have them face a new, powerful enemy that threatens the balance of the Pokemon universe, and they have to combine their unique abilities to defeat it.
Perhaps the trio stumbles upon a prophecy that predicts the end of the wizarding world. They then have to search for clues all over the wizarding and Muggle worlds to stop this from happening. They might also encounter a group of rogue wizards who are trying to use dark magic to create a new world order, and the trio has to stop them before it's too late.
Maybe Jesse Pinkman travels back to a time before he met Walter. He could then avoid getting into the drug world altogether. He might use his knowledge of the future to help other addicts get clean or work on some kind of community project to prevent drug use in his neighborhood. This would be a very different take on his character's story.
One idea could be a time - travel plot where the Golden Trio goes back in time to prevent certain dark events from ever happening. They could change the course of history and save many lives. Another could be a story where they have to face a new, powerful dark wizard who is even more cunning than Voldemort, and they have to rely on their unique skills and friendship to defeat him.
One idea could be a time - traveling adventure. The Super Trio (let's say Goku, Vegeta and Gohan) get sent to a different era in the Dragon Ball universe, like the age of the Saiyans' home planet. They have to deal with the primitive Saiyan culture while also trying to find a way back home.
One idea could be a story where the Lake Trio's powers are being misused by an evil organization. A young trainer discovers this and teams up with the Lake Trio to stop them. For example, the organization might be trying to use Uxie's knowledge - granting power to create a super - weapon.
One idea could be a story where the Lake Trio unites to stop an ancient evil that has been awakened in the Pokemon world. They could use their unique powers of willpower (Azelf), emotion (Mesprit), and knowledge (Uxie) to fight the darkness.
There could be a fem bad touch trio fanfiction where they are in a school setting. They get involved in a mystery, like trying to figure out who is stealing important items from the school. Each character in the trio might have their own unique way of investigating, leading to an exciting story.
Adventure is also a big theme. Since they are such dynamic characters, they are often put into exciting adventures, exploring new areas in the Undertale world, fighting off monsters or solving mysteries.