Just hop on the internet superhighway
Now through January 14, 2015, Pokémon Omega Ruby and Pokémon Alpha Sapphire players can claim a free shiny Beldum via in-game internet distribution. No GameStop visit necessary!
The Pokémon comes with its Mega Stone so, eventually, you can have your own shiny Mega Metagross. The X on its face turns from yellow to blue during the Mega Evolution process for what I’m sure are highly scientific biological reasons and not because “damn that looks cool!”