Everyone who contributed to the “Trade Pokémon at the GTS!” global mission in Pokémon Sun and Moon can now receive 2,000 Festival Coins. Players who registered a Game Sync ID at the Pokémon Global Link (PGL) before the mission ended earned double Festival Coins (4,000). To receive your prize, speak with the global mission receptionist in the Festival Plaza castle where you signed up for the global mission. In addition, PGL members who traded at least five Pokémon are eligible to receive five Rare Candies and a Friend Ball. Log in to the PGL using the game that you used to participate in the global mission to get a code for these items.
Source: Pokémon Global Link
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