Well, a cool plotline might involve a group of friends who discover a new type of pokemon battle that no one has seen before. They have to figure out the rules while also facing off against a rival group who wants to use this new battle style for their own gain. It would be full of mystery and action.
In some pokemon battle fanfiction, there could be a plotline where a pokemon has a special ability that is only revealed during a battle against a powerful enemy. This ability changes the course of the battle and the entire story. Maybe the pokemon has the power to temporarily transform into a super - powerful form, and the trainer has to learn how to control this new power to win battles and save the day.
One exciting plotline could be a battle between Naruto and a powerful new villain who has the ability to control time. This would force Naruto to use his skills in new and creative ways.
One exciting plotline could be a battle where all the Hogwarts houses unite against a new dark force that even Voldemort feared. Another might be a battle that takes place in a different magical realm, with Harry and his friends having to adapt to new magic rules.
One exciting plotline could be Ash encountering a new and extremely powerful Pokemon that he has to figure out how to catch. Maybe it has unique abilities that no one has ever seen before.
One idea could be a trainer with an underdog pokemon that has a unique hidden ability. They enter the colosseum battles and slowly discover how to unlock and use this ability to defeat stronger opponents. Another could be a story where the colosseum has been corrupted, and the trainer has to battle not just for victory but also to expose the corruption.
The action and strategies. When the Pokemon use unique moves and the trainers come up with smart tactics, it gets really exciting.
One plotline could be Naruto starts in his own world, discovers a portal to the Pokemon world, and decides to explore it. He might start as a novice Pokemon trainer and quickly rise in the ranks using his ninja skills.
One exciting moment could be when the protagonist's underdog Pokemon manages to land a critical hit on Leon's ace Pokemon. It completely changes the momentum of the battle.
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.
One plotline could be that Ash uses his ability to speak to Pokemon to solve a mystery. For instance, a group of Pokemon are acting strangely, and by talking to them, he discovers that there is a hidden force affecting them. Another could be that he has to convince a powerful and angry Pokemon not to destroy a village by communicating with it on a deeper level.
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.