The April 2020 issue of CoroCoro includes the special serial code ☆And337 – which allows players to encounter and catch Gigantamax Corviknight via Max Raid Battles in Pokémon Sword and Shield. This Corviknight is equipped with the Hidden Ability Mirror Armor and the move Steel Beam. The code is good through May 14, 2020.
Source: The Pokémon Company
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