Well, if Ash starts with an Ekans, his team dynamic would be very different. Ekans is a snake - like Pokemon, and it might not get along well with some of the more energetic or flighty Pokemon at first. For instance, Pikachu might be a bit wary of it since they are so different in nature.
One possibility is that Ash's Ekans could be a special one with unique abilities. Maybe it has a hidden power that helps Ash in battles against stronger opponents. For example, it could have a super-effective type of attack that is not common among Ekans, like a special poison - type move that can paralyze opponents for a long time.
He might become more cautious. Usually, Ash is quite bold and rushes into things. But if he's in a Team Rocket - centered fanfiction, he'd likely be more careful as he's constantly surrounded by danger. For example, he'd think twice before challenging a new Pokemon or entering an unknown area.
He could have a Froakie. It's a common and cute starter in Kalos. Maybe also a Skiddo for traveling across the Kalos landscapes. And a Bunnelby would be a nice addition for its digging abilities.
Their dynamic can become more competitive in school. Since they are in an academic environment focused on Pokemon, they might strive to outdo each other in grades or in Pokemon battles during school - related events. For example, if there's a battle - grading system in their Pokemon class, Ash would be eager to show his battle instincts, while Serena would want to display her strategic skills.
One possible strongest team could be Pikachu, Charizard, Greninja, Lucario, Sceptile, and Infernape. Pikachu has been with Ash since the start and has a strong bond. Charizard is extremely powerful. Greninja has its unique form and great combat skills. Lucario is a very capable fighter. Sceptile was a strong addition to Ash's team in Hoenn. And Infernape showed great power in Sinnoh.
His physical abilities change too. He might be stronger and faster as a werewolf. This could lead to a change in his confidence level. He might be more bold in battles, but also more cautious as he doesn't want to fully expose his werewolf side. He has to find a balance between using his new powers and still being the Ash his friends know and love.
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.
It would change his journey a great deal. Firstly, having a shiny Charmander would make him stand out more. Other trainers would be more likely to challenge him, either to prove themselves against someone with a rare Pokémon or to try and get his Charmander. Also, trainers with more experience might offer to help Ash train his shiny Charmander, which could lead to new training techniques. In Pokémon contests, his shiny Charmander would be a show - stopper, giving him an edge in those aspects of his journey as well.
Growlithe could be a very loyal addition to Ash's team. It might have a more protective nature compared to some of Ash's other Pokemon. This could change the way Ash approaches battles. Instead of always going on the offensive, he might rely on Growlithe to defend the team first. Also, the other Pokemon on the team might look up to Growlithe's courage, which could inspire them to be braver in battles.
Ralts could make Ash more empathetic. Since Ralts is a psychic - type Pokémon that can sense emotions, Ash might become better at understanding the feelings of other Pokémon and people. This could help him in his journey to be a better Pokémon trainer.