Extra Pilot and Plane
At the title screen, press the following combination of buttons: Left-C, Down-C, Right-C, Up-C, Left-C, Right-C, Down-C.
Mao Mao
At the title screen, press the following combination of buttons: Left-C, Down-C, Right-C, Top-C, Left-C, Right-C, Down-C.
Unlock Spanky Dolphin
Complete all of the Bonus Stages to unlock Spanky Dolphin.