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There's some bonus missions in the ORAS demo that are randomly obtainable after finish the first 10 missions. Mega Glalie can be transferred to the ORAS games once they're released if you obtain one in the demo. Completion of the bonus missions don't seem to give anything besides a Nugget that can be transferred to the ORAS games.
For North America: Gamestop/EB Games/Gameplanet is giving out serial codes for Diancie in the XY games. The event lasts till November 16. It holds a Normal Gem, and not its mega stone, unfortunately.