L + R + A = Green
Finally got around to playing the New Super Mario Brothers for the DS (doing laundry with nothing better to do), and I actually finished it off. I of course waited for the end of the credit sequence to see if I got something good for it. After the credits the bottom screen showed many repetitions of "Select a file -> L + R + A =" and then a green Mario head silhouette, then a save prompt, which of course I accepted. And as I'm sure you've all figured out by now, if you load your game by holding L + R when you select your file, you get to play as Luigi. Luigi has always been my favorite, so this is way awesome.


