This article pertains to the beta elements of Super Mario Bros. 3.
Beta elements
There were going to be two new enemies called Gold Cheep Cheep (a golden version of a Cheep-Cheep), and Green Parabeetles (green colored Parabeetles). The Gold Cheep Cheeps would come in groups and swim faster than regular Cheep-Cheeps and the Green Parabeetle is a green Parabeetle that flies faster than normal ones, Gold Cheep-Cheeps appeared in New Super Mario Bros. Wii as smaller versions traveling around in schools. The game coding reveals an item-sized Toad icon among some of the game's suits; this is interpreted by several as a sort of "Toad Suit", although it makes no changes to gameplay when granted to Mario. - This has been recently proven to actually be a Hammer Suit with palette errors, and appears clearly in a "?" block in 7-8, giving Mario the Hammer Suit. [1] Designers also considered a power-up to turn Mario into a Centaur (half-man, half-horse), although this was rejected (Tilden 1990, 21).
Koopa Troopas and and Hammer Bros. were going to host the mini-games. They were replaced by Toad. However, it could also be possible that they were all around at the same time, but all got scrapped except for one due to memory size. There were also different kinds of mini-games, similar to the ones in New Super Mario Bros..
Finally, fifteen extra levels exist within the coding of Super Mario Bros. 3. Some of these are strange and unique, while others bear much resemblance to levels in the final version and were very likely redone as those. Also, the back of the box of some copies of Super Mario Bros. 3 depicts Mario traversing a hilly grassland stage with tons of Parabeetles and two Note Blocks about. This particular stage is not any of the lost ones present on the cartridge, nor is it in the final game. It could even be a press mock-up from Nintendo. The "special" boxes also feature a beta map of Grass Land.
A Koopa Troopa hosting an item mini-game in Super Mario Bros. 3. - Hammer.gif
A Hammer Bro. hosting a card mini-game in Super Mario Bros. 3. 
Super Mario Bros. 3's "Toad Suit" as it appears in the game's programming. 
Unused Mario sprites. - Super Mario Bros. 3 Beta Sprite.PNG
Unused castle sprites. 
More unused mario sprites.
- ^ The Mushroom Kingdom Accessed 25 March 2009