Minus World

The Minus World is a glitch level found in Super Mario Bros. and is arguably regarded as the most famous glitch in video game history. It is an underwater level (exactly like World 7-2 in geography and enemy locations) that cannot be finished (the pipe at the end is glitched and takes the player back to the start), meaning that once there, Mario or Luigi is doomed to lose all of his lives by either running out of time or being defeated by enemies. The level got its name from fans because, when in the Minus World, the top screen says that Mario is in World -1. This is because of a glitch in the panels displaying the numbers. The Minus World is actually World 36, but the game is displaying the blank graphic for the number 36, leading to -1.

Method
Mario can get to the Minus World by going to World 1-2 and standing on the pipe that leads to the Flagpole at the end of the level. Mario 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, Mario should move right, so that when he's 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 done correctly, he will automatically move through the pipe (without the screen moving) and then through the wall and into the warp room.

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 doesn't 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. If the player makes the brick wall on the far right visible, however, the glitch will end.

Famicom Disk System
In the Famicom Disk System version of Super Mario Bros., the Minus World is accessed the same way, but 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 and a floating, headless Bowser, as well as an overall glitchy palette for several objects.

It marks the only instance of an underwater flagpole (sans the flag), which can easily stop the game from progressing if touched too high or initiating a fireworks display; if reached normally halfway down or lower, however, this flagpole will actually take Mario to World -2, a level identical to 7-3. There is finally a World -3 after this level;  -3 is a version of World 4-4 that lacks its False Bowser and maze elements, is colored differently, and is filled with flying Bloopers that can be stomped for 1000 points. This behavior is otherwise unused, though nearly identical flying Bloopers would be featured in Super Mario Bros.: The Lost Levels.

Beating World -3 takes the player to the title screen as if the player had beaten the game. 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 Mario's second quest.

Virtual Console
The Super Mario Bros. that is available for download off both the Wii's and 3DS' Virtual Console is an exact copy of the original game, meaning that gamers can once again enter the Minus World.

All Night Nippon Super Mario Bros. / Super Mario Bros.:The Lost Levels
By using the same trick in All Night Nippon Super Mario Bros. or Super Mario Bros.: The Lost Levels, Mario will be transported through the end-of-level pipe and be able to progress to World 1-3.

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 Pipe will still take Mario to 4-1 as if the pipes were reached by walking along the ceiling. In Super Mario Bros. Deluxe, the ability to perform the trick has been removed entirely.

Hacking
If one uses a gaming tool that can set the level that Mario is on, the Minus World goes all the way to -8. These levels are the result of level layouts being loaded with the wrong tilesets, enemy layouts, and properties, and are very strange. Specifically, World -2 is a version of 3-4 with water graphics; world  -3 is a version of 3-4 with overworld graphics, and world  -4 is just a blank screen.

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 only has 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 existed 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 3.

Trivia

 * In Super Paper Mario, The Underwhere is called "World -1" by its residents.
 * The Donkey Kong Country 2: Diddy's Kong Quest 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.
 * In 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".
 * While this glitch is often used to access the Minus World, it also has a practical use. If one enters the middle pipe, the player is warped to World 5-1 instead of the Minus World, thus greatly advancing through the game.