For a fairly long period of time, the engaging in Pokémon cosplay, dres as each other!
The contest mechanic in the games is intended as a way for Pokémon to compete without fighting, and judges them based on their looks and other factors, such as choice of move to use. While the trainer in a contest often has to don a special costume in order to compete, the Pokémon generally don't. There was a special Cosplay Pikachu in the remakes, Omega Ruby and Alpha Sapphire, but it dressed up like human professions, not like Pokémon. The games have never featured a contest where Pokémon attempt to resemble each other.
In the Sinnoh-era episode "All Dressed Up with Somewhere to Go!", Ash and friends find out about a contest occurring in a nearby city and make a detour to participate. Unlike other contests, only one Pokémon can be entered, and it needs to be able to not only dress as, but imitate another species of Pokémon. The episode goes through a rapid cycle of Pokémon, each colored or decorated in such a way as to look like a member of another Pokémon species. Some are absurd, like a Gyarados trying to look like a Caterpie, while others are surprisingly good. Ash chooses Pikachu to enter, which does a whole imitation routine, while Dawn chooses Piplup (dressed as Weedle) and Brock chooses Croagunk (dressed as Politoed). Despite a disruption by Team Rocket, Brock ultimately wins the contest, and with it, the prize: a Pokémon Egg that would go on to hatch into Happiny.
Pokémon Cosplay Contests
Pokémon designs often focus on having a distinctive silhouette, so having Pokémon dressed up as each other tends to result in some very strange-looking Pokémon. Many of the combinations in the episode are worth a laugh, and the whole thing is really just some goofy fun. Fans who enjoy playing around with Brock achieved his dream of becoming a Pokémon Doctor.
The Pokémon Dress-Up Contest may be one of the weirdest contests in the Pokémon anime, but it's all in good fun. This kind of silliness is one of the anime's specialties, after all!
