New Super Mario Bros Cheats

Play as Luigi:
Hold L + R and press A to select a saved game file to play as Luigi in single player mode.

Easy Lives:
In world 1-1, grab the Mega Mario Mushroom and crash through the rest of the level as fast as possible. If you're quick enough, you can net 5 extra lives.

Secret Toad Houses:
Finish a world with your time ending in two identical digits (77, 88, 22, etc.). A Toad House will appear on the map.

Secret Challenge Mode:
Beat the game. Start the cleared game file and pause the game. Press L, R, L, R, X, X, Y, Y and you should see the message "Welcome to the Secret Challenge mode". This mode works like the old Super Mario Bros., where you aren't allowed to backtrack to the left in any level.

Different Backgrounds;
Once you've beaten the game, start the cleared game file. In world 1, you'll see an new blue Toad house. Enter it to see four backgrounds for the touch screen that can be purchased with star coins. A fifth background is unlockable after collecting all star coins, completing all stages, and finding all hidden exits.

Bullet Cowboy:
If you're Mini-Mario, you can jump on top of Bullet Bills and ride them, sometimes across entire levels.

Get to World 4:
Beat World 2 as Mini-Mario.

Get to World 7:
Beat World 5 as Mini-Mario.

Get to World 8:
Beat World 6 as Mini-Mario.

Warp Cannons:
Some stages have secret exits that lead to Warp Cannons, which fire you forward several worlds. Look below to see where you can find the Warp Exits, and where they will take you.

Thanks to Revolution Readers A.W.O.L, Codeman, njnjn, dj, faryego, and Bahamut420!