If you beaten the Pokemon league, you can scan a special QR code for the mythical Pokemon, Magearna. Here is the North American code for it. After scanning it, go to the Hau'oli Shopping Center and go to the antiques shop.

You scan 10 Pokemon. You can even scan the same one again and again. After scanning any 10 Pokemon, you go back to the non-camera mode and hold the A button. You'll see a silhouette of a Pokemon come up on-screen, along with that Pokemon's location written in text below it. It'll be in TEXT on the screen with the silhouette. You won't find it using Rotom's map. Which Pokemon it is that comes up depends on two things. Firstly, which day of the week it is. Secondly, which island you're on when you do the thing where you hold the button and the silhouette comes up. You can find which Pokemon will come up by using the chart that can be found on this page: http://bulbapedia.bulbagarden.net/wiki/Rotom_Pokédex#Island_Scan Scroll down a bit and you'll see it.