While talking about the development of Mario Kart 7, Hideki Konno revealed that they had to bring on Retro Games if they could ever hope to release the game this year.
At first the project was handled by eight people, however, many of those were then moved to work on the 3DS launch title Nintendogs + Cats. In an effort to keep the project going, Nintendo called upon Retro Studios for help.
In the past, Retro Studios has worked on classic Nintendo series like Metroid Prime and Donkey Kong Country. Nintendo announced that the studio would only be helping out with the Donkey Kong focused course, but since then Retro has worked on revamping all 16 classic Mario Kart courses.
Mario Kart 7 will come out December 2nd in Europe which is only a week away, so be sure to keep a look out.