Pause the game and type "RUSSIAN AIR", then unpause the game.  Press
'N' to skip levels.  This doesn't work on all versions.

                   *** Halfway and End Monsters ***

SNAIL:    Shoot at eye, avoid mines.

ALIEN:    Shoot eyes at either side at top.  Scroll back and shoot
          center eye.

SPIDER:   Destroy as much web as possible.  Fly down to face spider
          and fire continuously.

CRAYFISH: Travels in figure eight.  Stay below and fire in it's
          face.

SNAKE:    Attacks from left of screen.

DRAGON:   Shoot the side heads first, then tail, then main head.

HEAD:     Shoot both eyes, avoiding laser fire and extending tongue.
          Shoot at head when tongue goes in.

TANK:     Use missles

GRAND SPACESHIP: Shoot all cannons until totally destroyed.