In this fanfic, the plot could be that Meowth has a change of heart after an encounter with a powerful and kind Pokémon that Ash helps. This makes Meowth realize that Ash's way of treating Pokémon is better. So, he joins Ash. He could then use his unique skills, like his ability to talk, to help Ash in battles and communicate with other Pokémon more effectively.
Meowth joining Ash in a fanfiction could also lead to some interesting character development for both. Ash might learn more about the Pokémon world from Meowth's perspective, especially the seedy side that Meowth has been a part of with Team Rocket. And Meowth could learn about friendship and loyalty in a new way, different from what he's experienced with Jessie and James.
If Meowth joins Ash in fanfiction, it could lead to some really interesting character dynamics. Meowth has been part of Team Rocket for a long time, so there would be a lot of room for him to change and grow. He could teach Ash some of the sneaky tricks he learned from Team Rocket, but in a more positive way. Maybe they'd form a new team and compete in different Pokémon competitions.
His personality might become more positive. Instead of being a bit of a schemer like he was with Team Rocket, he could become more helpful and honest. He might start to care more about others' feelings.
One possibility could be that Ash is initially deceived by Team Galactic's false promises of creating a better world for Pokemon. He might be drawn in by their grand talk about power and a new order. For example, they could convince him that their plans for using the power of the legendary Pokemon would benefit all Pokemon in the long run. However, as he spends more time with them, he starts to notice their more sinister motives, like their disregard for the balance of nature and the harm they are actually causing to Pokemon habitats.
The storyline would likely become more complex. With Meowth around, there would be a new dynamic. His loyalty would be split between Ash and his old Team Rocket pals at first. This internal conflict could drive parts of the story.
Well, it could be about a Meowth that discovers a special power that allows it to mega - evolve not once but twice. Maybe it goes on a journey to find a way to control this new - found power. Along the way, it meets other Pokemon and trainers who either help or hinder its progress.
Well, in the fanfiction, perhaps Ash catches Meowth to try and reform it. He might see that Meowth is not really a bad Pokémon at heart, just following the wrong crowd in Team Rocket. So he takes it under his wing, and they start to develop an unlikely friendship which changes both of them for the better.
Well, one possibility could be that Meowth betrays Team Rocket. Maybe he gets tired of their constant failures and decides to side with Ash and his friends. He might see that they have a more positive and successful approach to their Pokemon journey.
Ash joining Team Rocket could lead to some interesting character dynamics. He might start to question his own values. For instance, he's always been about friendship with Pokemon, but Team Rocket is more about using them for gain. This internal conflict could be a major part of the fanfic. Also, his relationship with Jessie, James, and Meowth would change drastically.
In a fanfic, Meowth's evolution might be a result of a magical spell gone wrong. Instead of evolving into a normal form, it becomes a hybrid of different Pokemon types. This new form gives it strange and wonderful abilities, like being able to turn invisible or create illusions. But it also has to deal with the confusion of its new identity and how other Pokemon and humans react to it.