At today's E3 press briefing, Nintendo announced that Kid Icarus: Uprising will sport 3v3 multiplayer, which will be demoed this week at the event. The game is also said to use the 3DS' augmented reality cards in an unspecified manner. Like most of the other 3DS announcements today, it's due later this year.
Nintendo's press conference is still ongoing. Shacknews will update as more information becomes available.