Secret challenfe mode
After you have finished all the worlds levels, (don't need to collect all the star coins for this) press start and enter the following: L, R, L, R, X, Y, X, Y.
It will come up with a message saying you have entered challenge mode. The only difference is that you can't go back in the level like the classic games e.g SMB
If you need more help, we've got more New Super Mario Bros cheats and also check out all of the answers for this game
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