Super Mario Bros. 2 is the sequel Super Mario Bros. Game, and houses some Beta Items within.
A prototype Version of the game was found and bought for $350. For Elements from the prototype, see here.
The final game contains leftovers from the Japanese version of the game, Doki Doki Panic, but only a few were found. In the ending scenes a Magic Lamp, a Heart, and a platform with a Lock can be found, which are all used in doki Doki Panic.
In Desert Stages, a small smiling face can be found, but it never appeared in Doki Doki Panic or the game's Prototype.
A cut text can be found in-game through hacking, it is called "ZELDA".