You'll Get Donkey Kong if You Buy a Digital Copy of New Super Mario Bros 2

In Japan, when you buy the digital copy of either the New Super Mario Bros. 2 or 5 Minute Demon Training, you are eligible to receive a free download of the origianl NES version of Donkey Kong. Check it out after the break for more information.
As reported by Wired, this is all part of the marketing push to increase awareness of the presence of digital downloads of games that are also available in physical retail.

This free Donkey Kong game is special in its own right because it has the extra stage that was removed in the initial release of the game back then. This version of Donkey Kong was never sold anywhere except that it was included as a freebie for those in Europe who bought the red Wii in 2010 (the Mario 25 years edition.)

Source - Wired
Click on the tags above to search for articles about specific games. :)