Something Nintendo did to take advantage of the capabilities of the 3DS, hit on social media outlets, and just provide a really cool addition to the game was make certain things available via QR CODE.
This started with the Club Nintendo promotion to get the "full Yoshi costume" for your Mii:
I started not to post that (and encourage you to sign up for Club Nintendo), but since it was already out and even Nintendo posted it on the Mario Tennis Facebook site, I figured it was okay. That said, if you are not a Club Nintendo member you are missing out...big time! (Side note: June 30th is your last chance to hit "elite" status (Gold or Platinum) and earn the super-secret, "special" gift!
As if the Yoshi Costume wasn't enough, they also added in a lot of Yoshi options...a fan request. I personally would have liked to see a few different characters, but I sure won't complain...this was a very cool touch, FREE, and something I hope that they will continue to do to capitalize on new games and make them that much more memorable.
They are actually dividing the QR Codes up by regions, so while the US got Yellow and Pink Yoshi right off, Europe got White and Black. If you are like me, you tried the "foreign QR Codes" just in case...and I can assure you, we will just have to wait for the Black and White Yoshi characters.
The Official Mario Tennis Open Site: http://mariotennisopen.nintendo.com/ either has the QR Code in place, or provides a subtle hint of where to find it...I was unaware until tonight that the Mario Tennis Open Facebook page had these nice and tidy QR Code segments. All we currently lack (that I know of) is Black and White Yoshi. I don't know for sure if this is an add on, or built in to the software, but it leads a lot of speculation for future releases. It would have been really cool to see this in Mario Kart 7.
Nonetheless, this is an unadvertised feature when you buy the game, and something that makes coming online and doing a little research worth the time. I can see this being a hot topic amongst younger players who debate "Black Yoshi" and wonder how their friend got it...accuse him of hacking the game etc...Good times Nintendo, good times!
Here they are in release order (North America)
Yoshi Costume for your Mii:
Black Yoshi=All Around