If you're in the United States, own a Nintendo 3DS and want Donkey Kong: Original Edition, all you have to do is... purchase and download the brand-new 3DS game Art Academy: Lessons for Everyone! or Crosswords Plus and register them before January 6.
Perhaps that's not the method you would have predicted.
And just what is Donkey Kong: Original Edition?
Nintendo's press release about Art Academy and Crosswords says: "Donkey Kong: Original Edition game for free. This is a special version of Donkey Kong with content never before seen in the U.S. and is not available for purchase."
The unofficial Super Mario Wiki, however, is a shade harsher: The game "was pre-installed for the European release of the Mario 25th Anniversary limited edition red Wii in 2010. This version restored some missing animations and the level 50M, which was cut from the NES version, although Donkey Kong mistakenly stands still in this level, and while the port's graphics are an improvement to the NES port, it is still inferior to the true arcade version, which remains unavailable on Virtual Console."
Donkey Kong: Original Edition was also recently offered as a free bonus to gamers in Japan who downloaded New Super Mario Bros. 2 and registered it with Nintendo.
Above: Donkey Kong: Original Edition, uploaded to YouTube by Arnold the Bartender