There is a secret code in the Japanese version of the game. Going into the menu screen and entering DOWN, UP, RIGHT, LEFT, SELECT, START, SELECT, START, B will trigger Toad to appear and say:
Secret code found!
Now, let's take a look at your Status.
Nothing's changed at all.
But, what about your experience points......
Nope, nothing's changed.
There's no point in looking for other codes,
and the result will always be the same.
I'll play with you as many times as you like, though......
Secret Code END
Contributed by Cavery210