The release date for PokÃ©mon Omega Ruby and Alpha Sapphire is drawing near. In the mean time, you can visit your local GameStop in order to receive two special PokÃ©mon for X and Y!
A shiny Gengar holding a Gengarite Mega Stone will be the first PokÃ©mon to be distributed. With the Gengarite Mega Stone, you'll be able to use a pretty shiny Mega Gengar in battle! The code card for this PokÃ©mon will be available between October 13 and October 26.
Immediately afterwards, a code card for Diancie will be available from October 27 until November 16. PokÃ©mon Omega Ruby and Alpha Sapphire will include the Diancite Mega Stone, so you will have to transfer your Diancie to those games if you wish to Mega Evolve it in battle.
PokÃ©mon Omega Ruby and Alpha Sapphire will be available for 3DS on November 21.
Source: The Official PokÃ©mon Website