Cheat mode:

Enter the password 0601. You'll get an invalid password message. Ignore it and press Start to return to the command center. Hold Select + A to get the Noisy Cricket super-gun. A lightning bolt will appear next to the number of lives remaining to confirm correct code entry. To fly around, press and hold Select + Up. To land again, press Down + Select.

Level skip:

Enter the password 2409 and start a new game. Now pause and press A to skip to the next stage, or press Select to skip the level.

View ending sequence:

Enter the password 1943 to see the end.