I think Lucario would be an interesting addition. It's a very intelligent and powerful Pokemon. It could sense danger and help Ash make better decisions. Also, Squirtle is a fan favorite. Its cute appearance and water - type abilities can add a lot of fun to the story, especially in water - related adventures.
For Ash, Pikachu is always a great choice as it's his most loyal and powerful partner. Alongside that, a strong flying type like Charizard could be useful. For Brock, his Onix would be a staple. And perhaps a water - type like Vaporeon could be good for him to balance his team. Since they are teaming up, having a psychic - type like Alakazam could also be beneficial as it can help in battles and also with communication in tricky situations.
Ash could also have Charizard. It's a powerful and well - loved Pokemon of his. It could provide a lot of firepower in battles. For Gray, a Glaceon would be great. Glaceon's ice - type moves could complement Gray's more strategic style. It could freeze opponents and give Gray time to plan his next move.
Pikachu is a very likely candidate. It's Ash's most iconic Pokemon and has a deep bond with him. Whenever Ash is in trouble, Pikachu often steps up to protect him.
Pikachu is a must - include. It's Ash's most iconic Pokemon. For Sawyer, his Slurpuff could be great. Also, Greninja for Ash would add a lot of action scenes. Sawyer's Sceptile could also be interesting to include as it can show the different training styles between them.
Pikachu is a must - have. It's Ash's most iconic Pokemon and can create some great interactions with Elesa's Electric - type Pokemon like Emolga. Zebstrika would also be great as it's one of Elesa's main Pokemon. And Luxray could be included as it's a powerful Electric - type that could have interesting battles with Ash's Pokemon. Plus, it would add more depth to the story as they strategize against each other or team up in battles.
I would recommend 'The Legendary Bond: Ash and Kyogre'. In this fanfiction, the author does a great job of showing the connection between Ash and Kyogre. It starts with Ash having a strange encounter with Kyogre and then evolves into a full - fledged adventure. There's also 'Ash's Encounter with the Mighty Kyogre' which is more action - packed and shows Ash in some intense battles while trying to protect Kyogre.
Well, I really like the fanfiction 'Ash and Dawn's Unseen Bond'. In this story, their friendship is explored on a deeper level. It has some really sweet moments between them. There's also 'The Great Tournament with Ash and Dawn' where they participate in a huge Pokemon tournament that you don't see in the regular series. It's full of exciting battles.
One great Pokemon Ash and Leaf fanfiction is 'The Adventure Beyond Kanto'. It shows Ash and Leaf going on an unexpected journey together outside of the normal Kanto region. They encounter rare Pokemon and face new challenges that test their friendship and skills.
I would recommend 'Ash's Kalos Adventure Redefined'. It has a great plot where Ash discovers a hidden power within one of his Pokemon. It's really engaging.