Gamestop will be distributing shiny (Mega) Gengar and Diancie this fall. If you go into their stores from October 13th to October 26th, you can receive a serial code to download a shiny Gengar holding Gengarite. It is the same Gengar that will be distributed in Japan later this month. The Gengar is meant to celebrate both the Halloween season and Phantom Forces.
From October 27th to November 16th, you can also get a serial code to download Diancie for the first time. When you transfer Diancie to Omega Ruby and Alpha Sapphire, you can then obtain its Diancite to Mega Evolve it into Mega Diancie.