Minus World

The Minus World is a glitch level found in Super Mario Bros. It is an underwater level exactly like World 7-2 in geography and enemy locations that cannot be finished due to the pipe at the end being glitched and taking the player back to the start, meaning that once there, it is impossible to leave without getting a Game Over or resetting. The glitch got its name from fans because the world-level screen displays as World -1. This is because of a glitch in the panels displaying the numbers. The Minus World is actually World 36-1, but the game displays a blank graphic for the number 36, so all the player can see is the -1. Total levels in the game (with bugs, including this one) - 256. The glitch was first described in the 3rd issue of Nintendo Power, and was later featured in its 100th issue.

Method
The player can get to the Minus World by going to World 1-2 and standing on the pipe that leads to the Goal Pole at the end of the level. Then, they should move to the far left end of the pipe, then duck while facing left. While ducking, the player should jump. While in the air, the player should move right, so that when Mario (or Luigi) is about to come back down, he should be just under the ceiling next within this moment. It may take the player several tries, for Mario must land in an exact spot on the pipe in order to travel through it. If this is done correctly, he will automatically move through the pipe (without the screen moving) and then through the wall and into the warp room. If not even one pixel of the pipe is showing, Mario will be trapped until the timer runs out.

Another method of reaching the Minus World involves Mario breaking two blocks on the ceiling, leaving the one on the far right. He should move to the far left end of the pipe and jump to the right. He does not have to duck as he can try to hit the bottom left portion of the block (without actually destroying the block). This should glitch the game, allowing Mario to get through the pipe and wall, but doing it this way is potentially more difficult and time-intensive.

If everything is done properly, Mario will see the three pipes in front of him from the Warp Zone. If he enters the pipe to the far left or far right, he will find himself in the Minus World. If he goes in the pipe in the middle, it will bring him to World 5-1. (This has a practical use, however, as it advances the player further than the normal Warp Zone would, although it is not used in speedruns as it skips past World 4-2, which has a Warp Zone leading to World 8.) If the player makes the brick wall on the far right visible (where the "Welcome to Warp Zone!" message appears), the Warp Zone will be correctly loaded and the glitch will end.

The reason the middle pipe leads to World 5-1 is that the game is loading data from the World 4-2 over-the-top Warp Zone (not the one above the vine) that has only one pipe to World 5-1, and it does not realize that the player is in the World 1-2 Warp Zone until the room is completely loaded, i.e., the brick wall becomes visible. The other two pipes in that Warp Zone are blank and registered as "36" (the number used for blank tiles in the game), causing the game to lead to World 36 when the player enters the world, hence the Minus World.

It is not possible to enter the Minus World from either of the Warp Zones in World 4-2. Through hacking, the pipes in the zone above the beanstalk are shown to lead back to the beginning of that section while the pipe leading to World 5-1 functions normally.

Family Computer Disk System port
In the Family Computer Disk System version of Super Mario Bros., the Minus World is accessed the same way, but it is very different in design. World -1 is just like World 1-3 but with underwater gameplay (despite lacking actual visual water) and featuring bizarre elements such as multiple floating Princess Toadstools that have no hitboxes, a floating headless Bowser, a misplaced Hammer Bro, as well as all objects using the "underwater" palettes (that is, green is replaced by gray), causing odd visuals.

This marks the only instance of an underwater Goal Pole (without the flag), which can easily stop the game from progressing if touched too high; if reached halfway down or lower, this flagpole will actually take Mario to World -2, a level identical to World 7-3. However, if Mario is to die on this level after passing the checkpoint, he will spawn beneath the bridge there, causing him to instantly die again, the process repeating until the player receives a Game Over. There is finally a World -3 after this level; World -3 is a version of World 4-4 that lacks its fake Bowser and maze elements, is colored underground, and is filled with flying Bloobers that can be stomped for 1,000 points. This weakness is otherwise unused due to Mario having different physics underwater, though it does appear in Super Mario Bros.: The Lost Levels. In addition, upon the player completing the level, although Toad's message of "Thank you, Mario! But our princess is in another castle!" still plays, Toad himself is missing.

Beating World -3 takes the player to the title screen. If the player starts the game again after going through the Minus World, it will replace all Goombas with Buzzy Beetles and will be like Hard Mode, as if the player cleared the game.

VS. Super Mario Bros.
In the arcade version of Super Mario Bros., which is harder than the original home console version, some bricks located above the end pipe are removed to prevent the trick from being performed.

However, it is not impossible to access. It can be accessed by clipping through the bricks under the pipe or the pipe itself. This version of the Minus World resembles the underwater portion of World 6-2. This room is actually the first level to exist in the Super Mario Bros. code in all versions.

Super Mario Bros.: The Lost Levels
Attempting to do this with the Warp Zone pipe to World 4 in World 1-2 of Super Mario Bros.: The Lost Levels will lead to two possible outcomes. First, it can send Mario or Luigi to the bonus area in another part of the level. Second, it could send him back to the underground bonus area of World 1-1. The game will still recognize the level as World 1-2 and the time will not reset. Completing it will send the player to World 1-3.

All Night Nippon: Super Mario Bros.
By using the same trick in All Night Nippon: Super Mario Bros., if Mario enters the leftmost pipe, he will instead be transported through the end-of-level pipe and be able to progress to World 1-3. If he enters the other pipes, he will be sent back to World 1-1, but it will be labeled 1-2 with the time not having been reset and all pipes hosting Piranha Plants. If he completes this level, he progresses to World 1-3, but dying sends him back to the real World 1-2.

Super Luigi Bros.
The Minus World can be entered in Super Luigi Bros. found in NES Remix 2; however, due to Luigi's higher jumps, it is trickier to do so than in the original game. Like the rest of this mode, it is mirrored so Luigi has to swim from right to left.

Speed Mario Bros.
Speed Mario Bros., a version of the original game that plays twice as fast, is a mode found in Ultimate NES Remix. The Minus World here behaves like the rest of the mode.

Removal
The Minus World glitch has been removed from remakes of Super Mario Bros. In Super Mario All-Stars, if the trick is performed, the Warp Pipes will still take Mario to their respective worlds as if the pipes were reached by walking along the ceiling. In Super Mario Bros. Deluxe and Super Mario Bros. 35, the ability to perform the trick is removed entirely. However, the glitch remains in the Virtual Console ports, in Nintendo Entertainment System - Nintendo Switch Online, and in Game & Watch: Super Mario Bros., as they are direct emulations of the original game.

Hacking
If one uses a hacking tool that can set the level that Mario is on, the Minus World goes all the way to -9. After -9, it changes to -A, later to -B, -C, and so on. After the letters, it changes to random bits of the terrain of all the levels. There are 215 of these bits. These levels are the result of level layouts being loaded with the wrong tilesets, enemy layouts, and properties.

Specifically, World -2 is a version of World 3-4 with water graphics; World -3 is a version of World 3-4 with overworld graphics, and being loaded with random enemy layouts, sprites, and properties. World -4 and World -5 are both black screens. World -6 is a glitched-out level that appears in a World 6-3 theme. Some gray bricks may be found on the edge of it, and a white Goomba will fall into the pit. The entire level is a pit, so Mario loses a life instantly. World -7 is a copy of World 3-3. After the player passes it, the game takes them to World -8, which starts off using the intro for World 1-2, World 2-2, World 4-2, and World 7-2, although the game blacks out after Mario reaches the pipe. World -A is a castle level that Mario cannot move in, and -9, -B, and -C are a black screen. All the levels after -4 can be played only by using cheats or hacking.

As shown in some editor utilities, the first Warp Zone that can take the player to the Minus World initially loads the data for the second Warp Zone, which normally has only one Warp Pipe in the center, until the "Welcome to Warp Zone!" message appears. The two empty slots on the left and right sides would read "36" if a graphic were to exist for that number. If two additional pipes are added in the appropriate places in this Warp Zone, they send Mario to the Minus World without executing the glitch. This explains why the second pipe, if the player performs the glitch, takes the player to World 5 instead of World 3 or the Minus World.

References in other games

 * Donkey Kong Country 2: Diddy's Kong Quest: The manual's description for Minus Barrels makes a Minus World reference by jokingly attributing them the ability to send the player to the Minus World.
 * Super Paper Mario: The Underwhere is called "World -1" by one of the residents.
 * Super Smash Bros. Brawl: On Smash Bros. DOJO!!, the official Super Smash Bros. Brawl website, there is a screenshot showing a list of friends to whom Target Smash!! replays can be sent, with one of them nicknamed "World -1".
 * Mario + Rabbids Kingdom Battle: one of the weapons, the Splatformer, references the Minus World in its description.

Trivia

 * The game actually has 256 worlds in total; however, worlds past 8 and 0 (World 0-1 is an underwater version of World 4-4) are glitched and reuse pointers from other levels in the level data. The Minus World (36) is the only one that can be accessed legitimately in the Western versions. These levels caused a rumor in Japan where a lightning strike on a Family Computer is said to create a Super Mario level never seen before, thought to be part of a secret World 9 (9-1 is an underwater version of World 6-2 that requires waiting a little to complete). However, the other glitch levels can be accessed in the Japanese version due to differences in the Family Computer hardware. Most versions also feature differences in those glitched worlds, be it different enemy placement, differently placed levels, as well as completely new ones not available on other ports. World 9 in The Lost Levels was inspired by this glitch.
 * A method of accessing these worlds involves swapping cartridges with  while the power is on, which can potentially damage the console's hardware. This glitch is due to the coincidental usage of the same RAM area between the two games that prevents a fail-safe from clearing the value which would normally store the most recently played world, which is used when holding the A button down on the start screen to continue a world after a Game Over. This value is overwritten by the "footstep counter" in Tennis.
 * One of the 256 worlds is a double negative world (World --1), which is actually World 40 since the first minus represents the number 40.