Pokemon Tretta is an arcade game over in Japan, and now players can sync up the arcade game to their 3DS with the Tretta Lab free app. But you're going to have to buy a gigantic peripheral that can attach to either the 3DS or 3DS XL for about $40 in order for the free app to be of any use.
You'll then have to spend more money to obtain tiles that contain specific Pokemon on them. You'll insert these tiles into the device, and from there you can view your Pokemon, compare different Pokemon, or send your pocket monsters to fight. So it's basically like Skylanders, or the other Pokemon game that's a blatant copy of Skylanders. Except, you know, not as fun looking.