New Super Mario Bros. Glitches

Glitch World
Once you have beaten the game (defeated Bowser once and collected all Star Coins in all worlds) in one of the worlds, where the Mushroom House at the start should be a red, glowing dot (as you see when you haven't done that world). Go onto it and press A. You will be taken underground, then when you go through the pipe, you will arrive in a glitched world with glitched enemies. If you want to, get to the end of the level. Then, you will be taken back to the world map but the game will freeze. Do this as many times as you like!