Well, well, well! A debug mode has been cleverly found for Super Mario Bros. 3! This is a pretty sweet Debug Mode here, I must say!
To access the code, you need a Game Genie. The code is:
KKKZSPIU
There's a ton of things that can be done with this. Right on the title screen, you can choose the world you start out at by using the up and down arrows. Pressing "A" gives you five extra lives, and you can do this until you get the maximum of 99 lives! Pretty sweet, if you ask me. However, the sweetness doesn't end there.
When you go to the map screen, check your items. You will have one of every item in your possession, and the rest of your items will be filled with P-Wings! This is especially useful when combined with the "Re-use Items" code found in the manual.
But it gets even better...
On the main screen, you don't die when time runs out! Take your time to roam through the levels! There's no hurry at all. You can even select a power-up just by pressing Select! Incredible! Great for if you forgot to put on the appropriate power-up for the stage. Pressing "B" and Select gives you...THE SHOE! Hooray! For some odd reason, however, the shoe's graphics only look right in a stage with spinys, and another enemy that doesn't come to mind right off the bat.
That's all for the SMB3 Debug Mode!