On the way to Eterna City, Ash, Dawn, and Brock decide to stop and watch a Pokémon costume contest. They are extremely excited to watch it, and when they find out that the prize for winning the contest is a Pokémon egg, they decide to enter. Brock enters Croagunk as a Politoed, Dawn enters Piplup as a Weedle, and Ash enters Pikachu who will do impressions of other Pokémon. Meanwhile, Team Rocket is also entering the contest. As the first round gets underway, Ash, Brock, Jessie, and James all make it past, while Piplup accidentally uses Bubblebeam, making Dawn lose. As the final judging is about to begin, Jessie and Meowth decide to skip the contest and steal the Pokémon egg. (thetvdb.com)