How to Get to World 4 on Super Mario Brosby Leonardo R. GrabkowskiUpdated September 22, 2017
There are secret worlds in "Super Mario Bros." for Nintendo DS. These worlds--world 4 and world 7--can't be accessed with a cheat code. You can only get there by following the right steps.
Use your main navigation screen to go back to world 2 if you've already beaten it. If you haven't beaten it, follow these steps after you get there.
Complete world 2, but make sure you are mini Mario or mini Luigi before entering the castle to fight the boss. The boss appears after you enter the second door (in the sand world). If you aren't mini Mario, let the boss hit you once to return to mini Mario form.
Beat the castle boss, but do not take the power-up mushrooms. The world 4 castle boss is not difficult--just pounce on his head two times. Once you have beaten the castle boss in mini form, world 4 will be enabled in your world navigation screen.
To unlock another secret world, world number 7, defeat the castle boss in world 5 as mini Mario or mini Luigi.