Release of Super Mario Bros. 2 is completely different from its original Japanese counterpart. The Western version is actually a version of Yume Kōjō: Dokidoki Panic with a new storyline and protagonists swapped for Mario and his friends.
Subcon, the land of dreams, is under an evil spell thanks to Wart, so Mario and the gang must save the day. New creatures to defeat and plenty of nasty surprises await.
After each level, depending on the coins you collect, you can use them in the bonus game to collect extra lives.