Mega-Mega Meowth Madness! (Japanese: ハリマロンVSメガメガニャース！！Harimaron VS Mega Mega Nyarth!!) is the tenth episode of the XY series, and the 809th episode of the Pokémon anime. It first aired in Japan on December 12, 2013 and in the United States on March 22, 2014.
While our heroes are in Lumiose City, Serena suggests they visit Professor Sycamore before they continue their journey, and she’s even made a batch of delicious macarons for the occasion. At the professor’s lab, they settle in with a nice cup of tea, only to discover the macarons are missing! They find the basket of treats in a corner, guarded by a very hungry Chespin who isn’t interested in sharing.
Meanwhile, Team Rocket has been researching Professor Sycamore’s studies on Mega Evolution, and the villains decide that stealing his data would be a big boost to their schemes. They break into the lab grounds, grab the professor, and throw him in the back of their truck. He’s not alone, however—Bonnie and Serena manage to sneak aboard before they drive away. The girls get locked inside by accident, but Serena manages to leave a trail of broken macarons—which Chespin quickly sniffs out, leading Clemont and Ash to the villains’ hideout!
In the meantime, James has plugged Professor Sycamore’s data into a mechanical Mega-Mega Meowth, which attacks our heroes! Chespin lets Clemont know it wants to battle, but neither Chespin nor Pikachu can make a dent in the mighty machine. But then, the Mega Blaziken that rescued Ash when he fell from Prism Tower reappears, along with its Trainer, a mysterious man in a Blaziken mask. Mega Blaziken’s incredibly powerful Flamethrower leaves Mega-Mega Meowth charbroiled, along with the actual Meowth who’s been controlling it, and Team Rocket is sent blasting off again. As our heroes head back to the lab with the professor, Mega Blaziken’s Trainer is watching over them—now without his mask. It’s Meyer, Clemont and Bonnie’s dad!
At the lab, Ash, Serena, Clemont, and Bonnie are saying their farewells when Bonnie notices Chespin watching them. Clemont thanks the Pokémon for its help against Team Rocket and says they’ll meet again soon, but it seems clear that Chespin wants to come along! And so, with Clemont’s friend Chespin now part of the group, the journey to Cyllage City continues!
The scene begins with Ash and his friends returning to Lumiose City, while Ash is thinking about getting his second Gym Badge at Cyllage City. Serena makes a suggestion that they first meet with Professor Sycamore before departing, and everyone accepts the idea while Serena shows them her basket of baked macarons. Meanwhile, at an abandoned warehouse, Team Rocket, after failing to give Furfrou to the boss, watches a recording of Ash on Prism Tower and notices the Pokémon that saves him to be none other than a Mega Blaziken. Team Rocket then plans on making Meowth "Mega Evolve" to get Ash's Pikachu, while planning on stealing the research data from the Professor. While Meowth questions being able to mega evolve, James corrects Meowth that if they are successful in stealing the Professor's data, they can implement it into a mecha called "Mega-Mega-Mega Mecha Meowth".
Back at Professor Sycamore's lab, Professor Sycamore learns that Ash and friends are traveling together now. Serena shows Professor Sycamore her macarons, and Sophie, one of the Professor's assistants, says that they should have tea. Professor Sycamore goes back to studying the Pokémon at his lab, saying that he will be back to have tea and macarons as soon as possible. As Sophie announces the tea is ready, Serena goes to take the macarons out when everyone notices they're gone. As everyone wonders where they went, Sophie notices Chespin behind a plant eating all of the macarons. As she calls Chespin out for stealing them, Chespin stabs Clemont in the hand with his spikes, takes a handful of macarons and runs out. Sophie explains to the group that that Chespin is very gluttonous. Serena and Bonnie decide to check on the Professor.
Outside the lab, Team Rocket arrives outside the lab in their van and break into it. As Ash and friends hear the loud noise of the van breaking through the glass, Serena and Bonnie go to check on what's going on. As Team Rocket confronts the Professor, he remembers them from before, specifically the "talking Meowth." Jessie ends up trapping the Professor in a net and capture him inside their truck. Serena and Bonnie are accidentally captured inside the truck, but thanks to the leftover pieces of macaron left by Serena, Ash, Pikachu, Clemont, and Chespin are able to follow the path to Team Rocket's hideout. As Ash and Clemont are going in to rescue the others, Chespin accidentally alerts Team Rocket about their presence and activates their new mecha, the Mega-Mega-Mega Mecha-Meowth. Ash tells Pikachu to use Thunderbolt, but to no avail, until Chespin and Clemont pull the external plug. Meowth then activates the sub-energy supply. Team Rocket gains the advantage, until Mega Blaziken turn the tables with a powerful Flamethrower. Ash and Clemont take care of the rest with Pikachu and Chespin, finishing the machine off with a combination of Electro Ball and Pin Missile to blast Team Rocket off and foil their latest scheme.
Back at the lab, as Ash and his friends give their goodbyes to the Professor. However, before they leave, Bonnie notices that the same Chespin has been spying on them the entire time. Professor Sycamore then tells Clemont that Chespin wants to travel with him. Clemont asks Chespin if it wants to travel with him, and it agrees. Professor Sycamore gives him Chespin's Poké Ball, and Clemont recalls Chespin back to its Poké Ball, allowing Chespin to travel with them. The friends give their goodbyes to the Professor and continue traveling towards Cyllage City as the journey continues!