A really exciting plotline could be Ash getting a chance to time - travel. He could go back to the past and meet his younger self or even go to the future to see how far he has come as a trainer. Along the way, he would face challenges related to the different time periods and the Pokemon that exist there.
One interesting plotline could be Ash encountering a new and extremely rare Pokemon that has unique abilities. This Pokemon might initially be hostile but gradually form a bond with Ash as they overcome various challenges together.
One possible plotline could be Ash's discovery of his own latent legendary powers. Maybe he starts to exhibit abilities that are unique to legendary Pokemon, like controlling the weather or having an extraordinary bond with all types of Pokemon.
In the fanfiction, perhaps there's a plot where Ash has to save a legendary pokemon from an evil organization. He might use his experience and the trust of his other pokemon to rescue it. This would not only show his courage but also how much he values all pokemon, whether they're common or legendary.
Another possible plotline could be that Evil Ash is on a quest to conquer a certain region. Serena, with her own Pokemon, decides to oppose him. Along the way, they both discover new things about the Pokemon world and themselves. Serena might have to team up with other trainers to stand a chance against Ash's newfound power.
A plotline could involve a special Pokemon that both Ash and Paul are interested in. They might compete to catch it, which could involve a series of challenges and battles. Or, perhaps there's a new type of Pokemon training technique that one discovers and the other tries to learn from or outdo. This could create an interesting dynamic in the fanfic.
Another plotline could be Ash getting involved in some sort of virtual Pokemon world within the fanfiction that has unique rules and challenges. He could discover new Pokemon species that are exclusive to this gamer - themed world. This would add a whole new dimension to his adventures and his relationship with his existing Pokemon team as they all adapt to this new environment.
One interesting plotline could be Ash and Alexa going on a special journey to discover a new type of Pokemon. They might face challenges like difficult terrains and other trainers trying to stop them.
In some fanfictions, there could be a plot where Ash has to protect Lillie from a group of evil Pokemon trainers. This would show his loyalty and courage, and also lead to some exciting battles and adventures. And their relationship could grow deeper through this process.
One interesting plotline could be Ash coming back with a new and powerful Pokemon team, ready to take on new challenges in the Pokemon world. Maybe he has a super rare Pokemon that no one has seen before.
One interesting plotline could be Ash facing new and extremely powerful Pokémon that he has to strategize in unique ways to defeat. Maybe he discovers a hidden Pokémon species that has been lost for centuries and has to figure out how to befriend it. Another could be Ash getting involved in a Pokémon tournament with a much higher level of competition than he's used to, which forces him to rapidly improve his skills.