A Shiny Beldum will be waiting for you to download once you obtain Pokemon Omega Ruby and Alpha Sapphire, via the Mystery Gift option.
The Shiny Beldum is a level 5 and knows the moves Hold Back, Iron Head, Zen Headbutt, and Iron Defense. It also Metagrossite.
But don’t panic! You’ll have up to January 14 to download it if you don’t get the game until the end of the holiday season