Hidden Level:

Goto "Level Selection" or "Saved Game" screen and enter the following:

Down Up Z L Down Left Z Down

Finally choose a saved game or level and press Left

Additional Energy:

Goto "Level Selection" or "Saved Game" screen and enter the following:

C-Left L Z Down L Z C-Left C-Right

After entering the code choose level or saved game

Last Level:

Goto "Level Selection" or "Saved Game" screen and enter the following:

Up Down L Z Down Right Z Down

After enteriing the code choose level or saved game and press left