From Bulbapedia, the community-driven Pokémon encyclopedia.
A Contest Pass (Japanese: コンテストパス Contest Pass) is a key item that allows players to participate in Pokémon Contests. It has a drawing of an award Ribbon on it.
In the games
In Generation III
In Pokémon Ruby and Sapphire, a Contest Pass is required for entering Pokémon Contests. The item can be obtained by talking to the receptionist at the Verdanturf Town Contest Hall.
In Pokémon Emerald, a Contest Pass is not needed; instead, only a Pokéblock Case is required. The item is present in the coding, but cannot be legitimately obtained.
In Generation IV
In Pokémon Diamond, Pearl, and Platinum, all that is required to participate in Pokémon Super Contests is something formal to wear, given to the player by Johanna on entering the Contest Hall for the first time. The Contest Pass is, however, a dummied-out key item that can be hacked into the bag, though it will have no effect.
In Generation V
Like all other items present in the coding of Pokémon HeartGold and SoulSilver, the Contest Pass is present in the coding of Pokémon Black and White, but cannot be obtained without hacking, and has no use whatsoever.
In the anime
holding their Contest Passes
Contest Passes are also required to participate in Pokémon Contests in the anime, and it seems they can be obtained at any Contest Hall. There are also different passes needed for each region.
Contest Passes first appeared in All Things Bright and Beautifly!, where Jessie had her expired Hoenn Contest Pass renewed and Ash, May and Brock received their first Contest Passes.
May got her Kanto Contest Pass in The Saffron Con, while Brock got his in What I Did for Love!.
Ash and Dawn received their Sinnoh Contest Passes in Mounting a Coordinator Assault! along with a Ball Capsule and a few Seals.
May, Drew, Harley and Solidad obtained Contest Passes for the Johto region prior to A Full Course Tag Battle!.