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Shadow Pokémon are antagonists from the mobile video game Pokémon GO. They are Pokémon that have been brainwashed and unnaturally boosted by Team GO Rocket, causing them to become extremely hostile.
Team GO Rocket, in its quest for world domination, began corrupting Pokémon with dark energy, making them lose their minds and be in constant pain from their newly inflated strength. This mixture of mindlessness, pain, and abuse from their trainers caused the Pokémon to become hostile, feral monsters with dark auras and red eyes.
Team GO Rocket uses the Shadow Pokémon in battle, relying on their unnaturally boosted stats to cheat their way through Pokémon battles. Shadow Pokémon are taught two moves unique to only them: Frustration and Return, and attack using 20% more aggressive attacks. If the player defeats the Team GO Rocket Grunt, they will abandon their Shadow Pokémon. The player can rescue the Shadow Pokémon by catching it, and then use Stardust and Candies to purify it back to its original form. The player can also TM away Frustration from them during certain events.