Super Mario Bros. 3/Codes
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 The Lost Levels
- The lost levels in Super Mario Bros. 3 are unused, abandoned levels that were programmed into the game, but were deleted from the final version. Some of these levels feature lost enemies that are also programmed into the game. The level that sheds some light on the subject is the level that can be accessed with the Game Genie code
AOZULT. This code forces entry into a lost level found inside the START panel in World 1. The level seems like it was deleted from World 6 for being too short and too easy. This is generally true of all the levels, especially ones matching motifs that appear later in the game. This suggests that these may either have been in the early stages of development before being deleted from the completed game, developmental versions of in-game, final cut levels, or may have served some other purpose such as use in conjunction with development tools.
Other codes include:
KZNUGGXE-OZNUIKUU, a lost plains stage similar to Worlds 3-9 and 5-3.
LZXUAGPZ-SINUGGXE-ELNUIKUL, a grassy, hilly stage featuring Goomba's shoe, Lakitu, a coin heaven and continuous Starman power-ups. Possibly an early version of World 7-3.
LZXUAGPZ-ZGNUGGXA-KLNUIKUL, an underground level with big doors and Buzzy Beetles. The layout of this level is reminiscent of World 1-5, but without the coin heaven. 
ZZXUAGPZ-GINUGGXA-NLNUIKUL, unused Tanooki Suit bonus rooms with castle music. 
GZXUAGPX-XLNUGGXE-NLNUIKUL, an auto-scrolling underwater ice level reminiscent of World 6 with Jelectros from World 7-4 and gold Cheep-Cheeps, an unused enemy in the final game. The middle of this level consists of an island filled with Munchers. 
AZXUAGPX-APNUGGXE-NZNUIKUU, a vertical level with waterfalls and pipes. 
IZXUAGPX-OZNUGGXE-KZNUIKUU, a cloud level filled with red Parabeetles and the unused, fast-moving green Parabeetles.
GZXUAGPZ-SGNUGGXE-SZNUIKUU, obviously a harder version of World 1-6.
GZXUAGPZ-KGNUGGXA-ELNUIKUL, another variation of the above level. No goal, cut short. 
IZXUAGPX-UZNUGGXE-SZNUIKUU, an unused cloud level. May be an attempt at a nighttime cloud level. 
GGNUGGXE-NZNUIKUL, an unused level, presumably an early version of a World 7 level. 
Caution: When using these codes, the pointers and enemies may load up incorrectly, or the screen may glitch all together and make the level unplayable.
 Miscellaneous codes
||Enables the debug mode.
On the title screen:
In the game:
||Mario (but not Luigi) can reuse his items infinitely|
||Allows you to enter any level, including levels that have already been beaten|
||Free movement mode on the world map|
||Grab ice blocks from anywhere, including solid walls|