The '?' card serves as the main form of player interaction, with the ability to pick from either playing a variety of mini games or 'summoning' one of the other cards. As you can see, the other cards feature characters from some of Nintendo's most popular franchises, and scanning any of these cards brings up their respective characters. Here's an image of some of the cards in action:
Considering the 3DS released in 2011, this was a pretty cool thing to pass a few minutes when you first got your system, though I personally find it to be a shame that they were just static models. You could change poses and the size of the models though, so that's pretty cool.
Luckily for me, though, Nintendo recently released 2 new promotional apps for the 3DS - Photos with Mario and, slightly later, Photos with Animal Crossing. Here are some videos of the two:
These apps are what the original 3DS AR cards started, but with a little extra greatness added in. Now, instead of the models just standing static, they interact with the 3DS's camera - making it look like they're interacting with the player. They can demonstrate different emotions and if you wanted to you could even move them away from the AR card that spawned them (providing the card is still on screen in some way). I think it's great that Nintendo went back and made these cards a little more exciting, as it was a shame that they were so uninteractive when the 3DS first released. That being said, it's not surprising that they were able to add more interesting features to the cards now as AR has developed significantly over the 5 years since the 3DS was released.
AR Cards used in Kid Icarus: Uprising
Another way that Nintendo have incorporated AR cards into their products is in the game Kid Icarus: Uprising for the Nintendo 3DS. This game had over 150 AR cards in total which could be collected by buying packs of the cards, or through various gaming magazines. Instead of being used like Nintendo's regular AR cards, these cards had the ability to actually interact with each other and battle. Here's a video of them in action:
The only downside is that once the cards are battling, it's more of a case of sitting watching them battle it out - the player can't resume interaction with the game until the battle is over. It would be cool if in future Nintendo could revisit this and have the cards react differently, playing different movesets depending on player inputs.
Never the less though, this is still super cool! Seeing characters battle it out against each other in the real world is pretty amazing. :)