I have 2 Rumors: 1 for Super Mario Bros. and 1 for Super Mario All-Stars.
Minus World: The Minus World, I think was supposed to be like a testing area on the cart for non-freak Gamers(In that case Mario). Nintendo put it so that: You have to play it even if you're an experienced player. 2 Reasons for being canceled: 1. Gamers didn't like the idea of a testing level. The first level was easy enough. 2. A testing level would take up to much space. NES had only about 4-bit sized games, so Nintendo took to much space.
SMAS: Super Mario All Stars is made of: Super Mario Bros. 1, Super Mario USA, Super Mario Bros. 2, Super Mario Bros. 3. Sort've like what Sega did with Sonic Jam. There was ANOTHER Mario All-Stars Game! Super Mario World, was planned for it. This time, I have proof. My cousin used to own a SNES. She had Mario All-Stars with it and Mario World was in it!! Maybe they took it out for to much space, or the fact that SMAS was annoying.(My opinion only.)
