Cheats for New Super Mario Bros. on DS.
Play as Luigi:
To play as Luigi (instead of Mario) you will need to complete the game and save. Go to Select A File, highlight a saved game, then hold down the L and R buttons and press A.
Complete the game and save. Load the save file, go to the world map and press Start to pause. Press the following button combination:
L, R, L, R, X, X, Y, Y.
A message should appear if you did this correctly. Challenge mode does not allow you to scroll to the left (i.e. you cannot go back).