Just tried the QR code on my JN3DS in Moon, says 'This QR Code cannot be scanned until you've become the champion'
EDIT: Pictures of the QR function instructions added.
[ATTACH=CONFIG]13845[/ATTACH][ATTACH=CONFIG]13846[/ATTACH][ATTACH=CONFIG]13847[/ATTACH][ATTACH=CONFIG]13848[/ATTACH]
This is NOT a mystery gift option, it's an in game option in your menu that essentially adds the location and preliminary dex info from what I can tell in the options info.