Note: You need the Nintendo Game Pokemon Pokemon X or Y and Internet conection in your 3DS / 3DS XXL
Add the grace and talents of the Shiny Pokémon Gengar to your game! Head to participating GameStop stores from October 27 to November 16, 2014, to pick up a special code card. When you enter the code into your Pokémon X or Pokémon Y game, you'll receive Gengar.
This Gengar will come holding a Gengarite Mega Stone, allowing it to Mega Evolve into a Shiny Mega Gengar.