Apparently, there will be "hundreds" of real life cards you can collect for the game, for use in the game's non-interactive augmented reality mode. With these AR cards, you'll be able to see animated character models come to life through your 3DS camera. Place two of these cards next to each other, and they'll battle.
The retail game includes six cards, so how you'll be able to acquire a collection of "hundreds" is baffling. Will they be sold separately in stores? And if so, why would anyone want them? Siliconera notes that Nintendo will hold "special events where you can trade, share and acquire new cards."
Here's a video of the mode in action: