Successfully complete the game. Start the cleared game file, then pause the game while at the world map and press L, R, L, R, X(2), Y(2). If you entered the code correctly, the message "Welcome to the Secret Challenge mode" will appear. 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.
