Gun power-up:
You will lose a gun power-up once you shoot one of the other humans. This is because when you lose a life, you lose your gun; and when you shoot a human, you lose a life.
Baby Aliens:
When you enter the building from the helicopter, shoot the exit sign when you see a purple alien, then shoot the first three lights. This allows you to shoot baby aliens before they form.
Chow Palace hints:
-When you reach the point where you fight the two grenade throwing aliens, kill them and the game will give you enough time to destroy everything around them. There are yellow drums and ammo crates at this location. There is a single alien and about fifty power-ups inside Chow Palace.
-Shoot all of the back windows in the warehouse after you destroy the helicopter to enter the bonus stage.
Tank Top:
Shoot the first fifteen windows on the right side of the hanger in wave two, right after you enter. You will need two players to do this, and you must use multiple views of these windows to hit them all. This entrance leads to a room called Tank Top.