Super Mario Bros. 2 (NES, 1988) 
It all started when the bigwigs at Nintendo of America decided that the game released in Japan as
Super Mario Bros. 2 would be too difficult for U.S. gamers. (And let's face it, folks, they were right.) Balking at the poor sales they anticipated from the release of such a game, NOA instead decided to give us something different. And in that, they certainly succeeded.
Doki Doki Panic was a game Nintendo had developed and released in Japan in cooperation with Fuji Television, in order to promote the latter's Dream Factory '87 event (an exhibition of Fuji TV's latest shows and related products). What was essentially a marketing tie-in would go on to much greater things, however, as Nintendo decided to upgrade, localize, and Mario-ize it for distribution in the West as
Super Mario Bros. 2.
For a game that stemmed from a project completely unrelated to Mario,
SMB 2 is responsible for introducing several characters that would go on to become staples of the Mario franchise, including Toad, Shy Guy, Snifit, Bob-Omb, Pokey, and Birdo.
In 1992, the game was released in Japan as
Super Mario USA, just as we Western gamers finally got to experience the Japanese
SMB 2 with the 1993 release of
Super Mario All-Stars. Now that's what I call cultural exchange!
In 2001, an upgraded version of
SMB 2 served as the GBA's flagship launch title in the form of
Super Mario Advance.