Meowth is now Ash's friend

 Pokemon Best Wishes! Ep. 43 (700th episode)

In BW042, while in Nimbasa City, Team Rocket prepared to put their latest plan into action. Later, in the next episode, Meowth was found injured by Ash, Iris and Cilan. While recovering, Meowth explained that while in Nimbasa City, he had botched up Team Rocket's scheme badly and was fired by Giovanni, leading to Jessie and James turning their backs on him. Later, Iris's Axew was kidnapped by a Scrafty, who wanted Axew's help to get its home back from a Mandibuzz. Using his ability to speak to both Pokémon and humans, Meowth not only helped get Axew back but also helped Scrafty get its home back and helped Mandibuzz return to her original nest. Afterwards, Meowth decided to travel with Ash and his friends, only for Iris to attempt to capture him in a Poké Ball. The capture nearly succeeded but Meowth broke out and told her he was going to help her regardless. Ever since, it seems to have become a running gag that he ends up in a Poké Ball at one point in an episode, as Iris tried twice (one of which was because Meowth didn't want a Purrloin to get caught), and by Cliff.