The original Japanese version of Super Mario Bros. 3 was released before the international versions and has some differences when comparing to them. The difference that affects gameplay the most is that, if the player gets hit when using a power up, Mario reverts back to Mini Mario. On the international versions, since this mechanic was deemed too difficult, when Mario gets hit when using a power up which is not the Super Mushroom, he goes back to Super Mario instead.
Other small level layout differences were made to made the game less punishing and also for bug fixes.