Big head mode
Successfully complete the game on the easy difficulty setting. Then, press X, A, Y, B(3), Up(5) on controller D when the game returns to the "Press Start Button" screen. If you entered the code correctly, you will hear a sound.
Mirror mode
Successfully complete the game on the normal difficulty setting. Then, press L, Left, L, Right, L, Down, L, Up, R, Left, R, Right, R, Down, R, Up on controller D when the game returns to the "Press Start Button" screen. If you entered the code correctly, you will hear a sound.