Get the Secret Ending
To get the secret ending, finish the game with at least 100 of the 101 Power Cells in your possession.
Hint - Biggee Your Jump
Press L1 + CROSS. If you timed it correctly, you will go into a crouch position and spring higher that you would by double jumping. Do the rolling jump, then just as you touch the ground, press CROSS. You will jump as high as the double jump. After double jumping, press CIRCLE rapidly for a longer jump.
Hint: No Falling Damage
Press CIRCLE to perform a spin kick right before you hit the ground to avoid falling damage.