The Pokémon could split into different groups. Some might stay by Ash's side no matter what, believing that he has a good reason for being with Team Rocket. Others would immediately distance themselves and try to find help from Ash's old friends like Misty and Brock. Over time, they might all work together to rescue Ash from the clutches of Team Rocket if they realize he's being forced or tricked into being part of them.
His Pokémon would probably be very confused at first. Pikachu, for example, might try to zap Ash back to his senses if he starts acting like a Team Rocket member. They would likely sense that something is wrong with Ash and would do their best to get him away from Team Rocket's influence.
The Pokémon League might condemn Ash's actions. Despite Team Rocket's wrongdoings, killing is not an acceptable solution in the Pokémon world which values friendship and co - existence. Ash could face consequences such as being banned from Pokémon battles or certain areas. On the other hand, some trainers who have been harassed by Team Rocket for a long time might secretly support Ash.
The Pokémon might initially think it's some sort of joke or mistake. But as time goes on, if Ash seems serious about being with Team Rocket, they could become divided. Some of the more headstrong Pokémon might leave Ash, while others might stay with him out of loyalty but still be unhappy about the situation. They would be constantly trying to nudge Ash back to his old ways of being a good Pokémon trainer.
Pikachu would probably be very confused at first. It's used to fighting against Team Rocket, not being on their side. It might resist and try to zap Ash to snap him out of it.
The Pokémon League would be in shock. They would see Ash and Misty as traitors and would probably send out teams to capture them. Pokémon trainers who looked up to Ash would be very disappointed. They might start to question their own values and the values of the Pokémon training world.
Yes, in some Team Rocket fanfictions, Ash can be depicted in various ways that might involve him having some sort of connection to Pokémon in a different light. Maybe he could be experimented on by Team Rocket to gain Pokémon - like abilities, or be transformed into a Pokémon - like being in a very creative and out - of - the - box fanfiction concept.
He was probably devastated. Ash had such a strong bond with his Pokémon. Losing them would be like losing part of himself. He might have initially been in shock, unable to believe what had happened.
It would also have an impact on the other villainous teams in the Pokémon world. They might see Ash joining Team Rocket as a sign that they can also recruit more powerful trainers. This could lead to more alliances between the bad guys and more complex plots to steal Pokémon and cause trouble all around the Pokémon world.
At first, his Pokémon would be startled. They've always known Ash as a human. But then, they would start to adapt. Some Pokémon, like Squirtle, might try to play with Ash in his new form, thinking it's a new kind of game. However, his more loyal Pokémon, like Greninja, would be determined to find a way to turn Ash back. Greninja might use its special bond with Ash to try and communicate with him on a deeper level in this new form, to understand what happened and how to reverse it.
Some of his more loyal Pokemon might try to resist the change. For example, Pikachu could use electric shocks to try and jolt Ash back to his senses. Pikachu has a strong bond with Ash and would be very confused and sad about his decision to join Team Rocket.
Well, Ash's Pokémon are a diverse bunch. His Heracross could use its Horn Attack to directly combat Team Rocket's Pokémon. Totodile could use its playful nature to confuse Team Rocket's Pokémon. And Ash's Bayleef could use its Razor Leaf to cut through any ropes or barriers that Team Rocket has set up to restrain Dawn. All of his Pokémon, with their unique abilities, would work together under Ash's command to save Dawn from Team Rocket.