New Super Mario Bros. Codes -

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

Secret Challenge mode:
Successfully complete the game. Start the cleared game file, then press to pause game play at the world map. Press , , , , (x2), (x2). The message "Welcome to the Secret Challenge mode" will appear to confirm correct code entry. Similar to the original Super Mario Bros. for the NES, Secret Challenge mode will not let you backtrack in certain levels. To indicate whether a level has a Secret Challenge version, the new right arrow icon will be lit in the top right corner of the map screen.

Special background patterns:
When you load a saved game file that you have completed the game on, you will find a new blue Toad House at the beginning of World 1. Inside are four background patterns you can choose for the touch screen. You can purchase these with Star Coins. The fifth and final pattern can be purchased for 20 Star Coins when you have collected all star coins, complete all stages, and find all hidden exits.

Saved game icons:
A star will be added next to your saved game file when one of the following tasks are completed. Completing more than one will display an additional star. The tasks are to defeat the final Boss, complete all world maps by finishing all levels and locating all secret exits, and spending all Star Coins.

Unlimited Toad House items:
When you load a saved game file that you have cleared every level, including the lettered bonus levels, Toad Houses will no longer disappear after you take the items. The only exception are the ones that appear based on your timer when you finish a level.

Alternately, if you want to have all of your Toad Houses back, save the game then intentionally lose all of your lives. When you return, all of the Toad Houses will be restored.

World 4:
Defeat the Boss in the last castle of World 2 as Mini Mario.

World 7:
Defeat the Boss in the last castle of World 5 as Mini Mario.

World 8:
Defeat the Boss in the last castle of World 6 as Mega Mario.

Mushroom house bonuses:
Complete a stage with a time having the last two digits of the same number to have a different color Mushroom house at the start of the World.

Have a time ending in 11, 22, or 33 for a red Mushroom house appears that awards items. 
Have a time ending in 44, 55, or 66 on the timer for a green Mushroom house with a mini-game for an extra life. 
Have a time ending in 77, 88, or 99 for an orange Mushroom house with a Mega Mushroom.