The official Pokemon website has announced new Pokemon distributions for the coming months. From October 13 to 26, a code card can be collected from participating Gamestop stores in the US, allowing players to download Shiny Gengar to their X or Y game. This Pokemon is also holding Gengarite allowing it to transform into the creepy white ghost you see above, just in time for Halloween!
Then, from October 27 to November 16, a code card for the legendary Pokemon Diancie will be available at Gamestop stores, also for X and Y games. Trading this Pokemon over to Omega Ruby or Alpha Sappire and finding the Diancite will allow it to Mega Evolve.
Source: Pokemon.com