Press Select + Start + A + B during game play.
Enter S6DJNB72 as a password.
Level 1-5: N4JZN5KZ
Level 2-5: &RG8NB&X
Level 3-5: XXG!NGI5
Level 4-5: ]MNHS?
Select one player mode, choose the Vs. option and the hard difficulty level. Hold L + Up and press A or Start. The screen will turn red to confirm correct code entry.
Press B, A, L(2) when Yoshi appears and says "Nintendo" in the opening sequence. A sound will confirm correct code entry
Select two player mode, choose the Vs. option, hold L + R on controllers one and two, and press A on controller two. To cancel, repeat the code and press B on controller two instead of A.
Hold L + R on controllers one and two for approximately five seconds at the player vs. player character selection screen. The question marks at the bottom of the player vs. player character selection screen will be replaced by images of the bosses.
Start single player versus mode game against the CPU. Defeat Lakitu and hold X + Y when the phrase confirming that he is free appears. A character selection screen will appear. This may be done after defeating each character.