Secret Exit In Level 2-3
On Level 2-3, the Dungeon level go to the bit where the water rises and quickly swim up to the room with all the coins. While the water is still up, there will be a switch. Quickly press it and swim up. This will lead to a secret exit. Complete the stage that opens and a pipe will open. This will lead you straight to Bowser's castle(the last boss in world 2).
More tricks, tips and cheats for this game are right here - New Super Mario Bros cheats
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