Well, it could mean that Ash is getting inspiration from the creativity in those old fanfics. Maybe he finds unique storylines or character interpretations that he can use in his own Pokemon journey, like new strategies or ways of bonding with his Pokemon.
It could also expand the lore. Old fanfics often have their own interpretations of the Pokemon world. When Ash uses ideas from them, it might introduce new concepts or relationships that weren't part of the original story. This can make the Pokemon world seem even larger and more complex.
You can start by looking on fanfiction.net. It has a large collection of Pokemon fanfics, and you're likely to find quite a few 'ash old pokemon fanfic' there. Just use the search bar and type in relevant keywords.
Some 'ash old pokemon fanfic' take a different turn and explore what would have happened if Ash had made different choices. For instance, if he had chosen a different starter pokemon instead of Pikachu. This kind of fanfic can be really exciting as it rewrites the whole pokemon journey in a new and unexpected way.
Maybe Ash's old Pokémon have unique skills that are rare in Kalos. So, he uses them to gain an advantage in Pokémon contests or battles. His Charizard, for instance, could be a formidable opponent against Kalos's dragon - type Pokémon, and this could lead to some exciting rivalries and plot twists.
Maybe Tracey. He was also an acquaintance of Ash. Since Tracey has his own unique skills and knowledge about Pokemon, his presence could bring new elements to the story. He could help Ash and other friends with things like Pokemon research or understanding some rare Pokemon behaviors.
I'm not sure about its popularity. It might be popular among some fans who like to see alternative and edgier takes on the Pokemon story. But it could also be quite controversial as Ash is such an iconic and generally well - liked character, and making him a cheater goes against the common perception of him.
In Ash's adventures in legendary Pokemon fanfics, he often has extraordinary encounters. For example, he might form unique bonds with legendary Pokemon that are not part of the main canon. These fanfics can take his story in new and exciting directions, like having him team up with a Mewtwo in a way that defies the normal Pokemon - trainer relationship. It's all about exploring the untapped potential of his character in the context of the amazing world of legendary Pokemon.
One of the popular fanfics where Ash calls the strongest Pokémon could be those where he summons Arceus. In some fanfictions, Ash might have a special connection with Arceus, the so - called 'God of Pokémon'. This could lead to epic battles and adventures as he teams up with the most powerful being in the Pokémon universe.