Key Items are items that are *mostly* needed to go past certain obstacles in the Pokémon Games and exist across all five Generations. Key Items are only found in the Mainstream Pokémon Games, along with both Pokémon Colosseum and Pokémon XD: Gale of Darkness.
In Generation I, Key Items were also added into the main backpack without being separated into its own compartment, making it possible to have the main backpack fill up faster due to carrying Key Items that aren't necessary at that point in time.
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