A Connoisseur's Revenge!
As Ash and his friends travel to Castelia City, site of Ash’s third Unova region Gym Battle challenge, they come across the grand opening of a huge new Poké Mart. It’s as big as a shopping mall!
Inside, they find a shop where a Pokémon Connoisseur is checking the compatibility between Trainers and Pokémon. Ash lines up to be evaluated as well, but just as he’s getting impatient with the wait, another shopkeeper invites him over. The proprietor is a girl named Burgundy, who insists that she’s a Connoisseur, too. But Ash gets suspicious when Burgundy says he should get rid of all his Pokémon because he isn’t compatible with any of them—even his best buddy Pikachu!
We then discover that she went up against Cilan at the Striaton Gym—and since her defeat there, she’s been holding a serious grudge. So, she studied to become a Connoisseur, then returned to challenge Cilan again. But by the time she got back, Cilan was already on his journey with Ash and Iris!
Burgundy challenges Cilan to a revenge battle, saying that if she wins, Ash has to give up all of his Pokémon. Ash is very worried, but Cilan accepts anyway, and in the process of defeating Burgundy, gently attempts to teach her the value of open-mindedness when evaluating Pokémon and Trainer compatibility. Angrily, she vows to come back again to beat Cilan, then stomps away. Ash is just happy that he can keep all his Pokémon, and they can again set their sights on the Castelia City Gym!