Before you ask: yes, it's a Gamecube controller. Of course it is. What else would it be?
This Arcade-y Basketball Game Brings The NBA Jam Vibes
Not content to play Smash Bros. with the 3DS, だいこん went ahead and modded their system so they could play using a controller. Honestly, when people are destroying their circlepads while playing Smash, can you blame them? It's probably such an improvement that all the cables become worth it. I say this as someone that's been playing the full game for the last week, and boy, what I would give to be able to play it like this!
I'll have something more in-depth about how the game controls on the 3DS sometime later this week. For now, we can all jealously look this mod. Sigh.