Nintendo will give Japanese customers a free copy of Donkey Kong for Nintendo 3DS for buying the digital versions of New Super Mario Bros. 2 or Demon Training, it said Friday.

The summer-long campaign is designed to spread awareness of Nintendo's new push for 3DS games being sold in physical form as well as digitally.

The free copy of Donkey Kong is notable due to its inclusion of an extra stage that was removed from the original 1983 version of the game for the Famicom. This so-called "original edition" has never been sold, although it was included as a freebie for European customers who bought the Mario 25th anniversary red Wii in 2010.

One surprising tidbit from the Nintendo downloading FAQ: Download codes for digital games must be redeemed within 150 days of purchase (or launch date, whichever comes last) or they expire.

Nintendo of America has not given any word about similar promotions. New Super Mario Bros. 2 will be released in the U.S. on August 19.