With the release of Pokemon Sun and Moon, two new free Pokemon promotions are running, for Munchlax and Magearna. These are obtained in different ways, as follows:
Munchlax (holding a Snorlium Z), available until 11 January: Simply load up the game and select Mystery gift > Get gift > Get via Internet
Magearna, available until 5 March: Less easy to get hold of, you first need to beat the game. Once you've done so, open up the QR code scanner and scan the code that I'll post in the first comment.
That's about all that there is to it - enjoy!