New Super Mario Bros. Hints & Cheats

At the "select a file" screen, keep pressed L and R buttons and choose one of your saved game files with the A button.
Now you'll play in the game as Luigi instead of Mario!

While paused on the map, press L R L R X X Y Y to enter the secret Challenge mode. You will now be unable to go back to an area that has scrolled off the screen while playing a level. This cheat only works after you finish the game.

To save your game anywhere on the map screen, beat the final castle in World 8. When you restart, you will have a star next to your save and you'll get the "Save" option added to your menu in the map screen.

If you beat a level with a time left of x11, x22, x33, x44 etc you get fireworks and the original mario level completion song will play.

The mushroom houses at the start of each world (the point with an arrow at the start) differ determining on the time you get on a stage.

If you get x11, x22, x33 on the timer, a Red Mushroom house appears, which generates items.
If you get x44, x55, x66 on the timer, a Green Mushroom house appears, which is a 1up minigame.
If you get x77, x88, x99 on the timer, a Orange Mushroom house appears, which lets you gain a Mega Mushroom into your inventory, thus overriding anything in it.

As you may know, jumping onto the flagpole at the stage's end will net you some points (up to 8000). In this game, if you somehow manage to jump high enough and land on the very top of the flagpole, you will automatically receive a 1-Up.

In some worlds, there are cannons you can access (usually through taking secret exits). When you enter the cannon area, there will be a large cannon in the area, and a world number written below it. If you want to warp, simply drop into the cannon and off you go! Here is a list of the known warp zones thus far:

World 5 Warp #1: Take the secret exit from the World 1 Tower.

World 5 Warp #2: Take the secret exit from Stage 2-A.

World 6 Warp: Take the secret exit from the World 3 Ghost House.

World 7 Warp: Take the secret exit from the World 4 Ghost House.

World 8 Warp: Take the secret exit from the World 5 Ghost House.