Alright, so here's the thing: Everyone is familiar with the concept of Super Secret Bases, right? If you add someone's base, you can visit their base and even battle them. Our friends in Japan took full advantage of this mechanic and created what is probably the best way to earn EXP in any pokemon game to date! As some of you already know, the amount of EXP you earn from a pokemon is based on their HP stat, so naturally the best pokemon to get experience from would be Blissey, but unfortunately for us, there never really were that many trainers carrying around high level Blisseys, and even fewer that you could actually rematch. Until now atleast. The imgur links i posted just below is of 12 scannable QR codes, all which will give you a super secret base containing a trainer that will triple battle you with 3 level 100 Blisseys that are each holding a Toxic Orb with no attacking moves whatsoever!
Secret Medow:
http://i.imgur.com/aF02xUQ.jpg
Secret Shore:
http://i.imgur.com/sXqmCUo.jpg
All you need to do is send out whatever Pokemon you want to level up, let the toxic damage kill off the Blisseys, and prepare to recieve an enormous amount of EXP points! Here's a step-for-step guide for those wondering exactly what to do
-Go to your PC in your secret base and go to "Manage QR Code patterns." Go to "Find a Secret Base." Scan the 12 posted QR Codes.
-If you have issues with scanning, try increasing your screen brightness or zooming in by simply clicking the picture.
-You need to be able to use the HM Dive to gain access to the Secret Medow and Secret Shore where these bases are located.
-You must wait until midnight the day after you scan the QR codes to interact with the secret base trainers.
-There will be 3 Blissey for each Secret Base trainer.
-Use the level release object in the base to make the Blissey level 100. (You must have obtained the level release object for yourself to activate it. It is found at Battle Resort in the homes to the far right of the Battle Maison past the bridge. Access to this area is only available after completion of the Delta Episode)
-It's highly advised to use Experience Point O-Power and lucky eggs for more EXP.
-You can only battle each trainer once a day unless you use the following method: You can battle the trainers twice by making them your Secret Pal and battling them in you base. After you are done, just remove them. You can repeat this everyday, battle them in their base, make them your secret pal, battle them in your base, then remove them. This lets you battle 24 Blissey trainers a day, but requires a little more work of course.