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"Most Poké Balls have difficulty recognizing Ultra Beasts as Pokémon due to their extradimensional origins, impairing their ability to effectively catch them.
Beast Balls, being specifically designed to catch Ultra Beasts, are instead ineffective against Pokémon that are not Ultra Beasts. The
Master Ball is unaffected by this impairment due to catching any Pokémon without fail, even Ultra Beasts. "