The immensely popular Pokémon franchise turned twenty years old earlier this year, and as part of the celebration, The Pokémon Company is distributing almost every event-only Pokémon this year, making some of the rarest Pokémon around readily available to fans. Darkrai was distributed back in May, but if you missed out the first time around, you have another chance.
The Pokémon Company has made Darkrai available once again, this time until October 31st. All you need to do to nab one is boot up a copy of any sixth generation Pokémon game and input the code “Darkrai20.” This is the same Pokémon that was given out at GameStop, so if you received that one, you won’t be able to get another one.
Source: The Pokémon Company