The Minus Zone
As most of you know by now, there is a minus world found in Super Mario Brothers original NES release. In the end of world 1-2, if you do everything just right, you will glitch the game, and be taken to this world. Below is the step by step way to do it.
1: You need to be Super Mario/Luigi, or Fire Mario/Luigi. This trick will only work if you are big.
2: Head to the final pipe, that will take you to the end of World 1-2. Instead of going in the pipe, stand on top of the edge of it.
3: Crouch down on the edge of the pipe. Then face left.
4: Now jump up in the air. (Stay crouched while doing this) When you jump, hold the right button to make yourself jump to the right.
This should make you get stuck in the wall. when you do get stuck, you will automatically be dragged to the warp pipes. Do not go so far as to make the "Welcome to the Warp Zone" appear. Instead, just hop down the first pipe to the left. This will take you to World -1. It is actually World 36-1, but for some reason the 36 does not appear.
This level is the exact same as World 7-2, only there is no other way out than to die. If you go through the pipe at the end, you will only come back to the beginning of the level.
In the Japanese version, there is actually three sub levels in this minus world. Once you complete the three levels, you will be taken back to the intro screen, as if you had beaten the game. You will be given the option of doing the regular or hard mode of the game.
Perhaps if I can find a Japanese ROM for the game, I can map out the other three levels.