Pokémon GO players who take part in raids during Pokémon GO Tour: Kalos – Global may receive one of three Special Backgrounds after a successful catch. The limited-time backgrounds are inspired by Pokémon X, Pokémon Y and Mega Evolution, adding a collectible visual bonus tied to the Kalos celebration. The special designs appear behind eligible Pokémon caught from raids during the event, giving Trainers an extra incentive to battle and complete as many raids as possible. It is a subtle but fun way to connect the in-game experience to the original Kalos-era themes.
Source: Official Pokémon GO blog
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