They actually arrived earlier. It's pretty hard to revise because they're literally different every time. They can be used in Animal Crossing New Leaf with a magic lamp to summon a character and either bring them to your town or give you an item. If the character isn't a villager (e.g. Isabelle or KK Slider), they can give you a self-portrait or some other item related to their character. Cards can also be used in amiibo Welcome Update games if you manage to get the Wii U or 3DS as game items through the Fortune Cookie system. They can be summoned to help you in mini-games, and their stats are placed on the map for easy reference. I believe these cards are also compatible with Happy Home Designer and Animal Crossing: Amiibo Festival, but I haven't played those games yet. and don't know much about their use there.
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