Enter ZZZCYX as a password.
Enter YAYAYA as a password.
2-2 - CBYXYC - 3-1 - XABXAB - 3-2 - AZCBXC - 4-1 - YYBBCY - 4-2 - BAXCXX
Enter XBABYX as a password. The word "Correct" will confirm correct password entry. You will lose energy, but no lives, during game play.
Move south after completing the objectives in mission 1, phase 2. Enter the alternate exit in the dead end canyon to start a bonus underwater mission.