After completing the crack of doom, pick the southern gate. Press start, hold L + R, enter B, X, B, Up. Then, enter X, Down, Y, A. You will be in perfect mode with infinity health. Beat ALL the enemies and beat the level. You will grow 4 levels or over(having all perfects).

Note: You do not have to enter the code B, X, B, Up but you will not have infinity health if you do not type it in.