To get the best ending for the game, shoot off all the paneles on the mothership.
At the beginning of the game, only shoot the first three STARR team members you see.
If you did it right the screen will turn green and you will have a night vision capability. In this mode, you are a mercenary from the Kronn hierarchy sent to sterilize Area 51 of the Kronn rebels. You will notice that the grenades, bullets, shot gun shells, and machine gun bullets have all taken on Kronn form. You will also gain 20,000 extra points whenever your score is tallied, and you can shoot STARR members at your own free will.
Level 2: Shoot out all of the upper windows of the far back wall in the hangar. Another can be found by shooting all the yellow barrels when you are in the forklift.
Level 4: Shoot every yellow box while you're riding in the jeep.
Level 5: Shoot the doorplate of the second door marked General Weatherby as the door is opening.
Level 7: Shoot all the yellow barrels at the first area where the four purple zombies are throwing barrels on the hill.
After riding through the air field and grabbing the ladder that's hanging from the helicopter, look closely for paintings hanging on the office walls. If you shoot all the paintings, and both office doors, a frightening, yet funny, room will be revealed.