Complete the game on all difficulty settings to obtain the "Thunder gun", which can kill everything in sight. When entering a loading screen or room, quickly tap [Fire]. The gun will fire in all directions. You will get a large health boost and all enemies will be killed.
Go to Episode 8 Part 3. At Mech-Nukem's left arm (the incomplete one), press [Up] close to the path in front of it. You will enter a secret area containing Wozma, the secret Boss. During this time you will have infinite ammunition.
ACHIEVEMENT - HOW TO UNLOCK Deworming the Big Apple (20 points) - Finish "Rooftop Rebellion". Confucius Say…Die (20 points) - Finish "Chinatown Chiller". Max Pain on the A-Train (20 points) - Finish "Metro Mayhem". I Love the Smell of Sewer Scum (20 points) - Finish "Unholy Underworld". Worker Safety, Last (20 points) - Finish "Fearsome Factory". This Ain't the Love Boat (20 points) - Finish "Tanker Trouble". Going Down Faster Than Enron (20 points) - Finish "Deviant Drilling". Space, the Final Frontier (20 points) - Finish "Orbital Oblivion". My Boots Are Made For Stompin' (10 points) - Stomp on 20 enemies. Pig Out (10 points) - Kill 75 enemies. Glow Like Dr. Manhattan (10 points) - Collect 120 Nuke symbols. New York Minute (10 points) - Finish the first level in under 3 minutes.