Berzerk

Harmless shot:
When robots shoot horizontally, any shot the hits your character in the space just below the head will not cause damage.

Evil Otto smashes through a wall:
Use this trick on any level that has a top door. Approach the door until your character's head is just out of the door, but not enough to cause your character to exit the room. Wait for Evil Otto to appear and press Select (or move around so Otto does not get your character before getting to your left or right side). Otto will disappear out the door before a "laser beam" shoots to the bottom of the screen. Otto will "smash" through the wall below and float, not bounce, towards your character.
Information in this section was contributed by Steven Lucas.

Random number display:
Press Select while a robot is exploding to display a random six-digit number at the bottom of the screen.
Information in this section was contributed by Steven Lucas.

Avoiding Evil Otto:
Never run from Evil Otto along the bottom of the screen. Otto will take smaller bounces and outrun your character.
Information in this section was contributed by Steven Lucas.

If you want Evil Otto to move slower when he appears, leave at least one robot alive. Evil Otto will move much faster if no robots are in the maze.
Information in this section was contributed by Chris.

Shooting around the world:
Note: This trick requires a maze with both a left and right exit. To fire a shot that goes around the world, move your character as close as you can to the exit on the right side. This should be so close that one more step will make the player exit to the next maze. Then, while facing the exit, press Fire button to shoot "around the world". The shot will seem to repeat itself at the edge several times. It will then come out the right side exit and continue to move for a short distance. This is a great way to safely destroy robots on the other side.
Information in this section was contributed by jup.

When you are in a maze with an exit on the right and left sides, stand just inside the exit and fire in the direction of the exit. If you are close enough, your shots will "wraparound" and come in the other doorway. Note: This may not work on some game modes.
Information in this section was contributed by Chris.

Avoiding shots:
When firing vertically, the robots shots always come from only one side. Stand just off-center on the opposite side and you can shoot them while their shots go past you harmlessly.
Information in this section was contributed by Chris.

Diagonal shot:
Hold the Joystick in a diagonal direction to shoot at an angle. You can kill robots easily this way, as they cannot shoot at an angle.
Information in this section was contributed by Chris.

Bizarre game play:
Note: The following tricks require a disassembled Atari joystick in order to activate two opposite directions at the same time.
Information in this section was contributed by Roy Tony.

Lose the gun
Hold Up + Down and tap Fire. At times, you will lose your gun. The gun will remain in one place and the robots can get killed if they walk into it. This may also work by holding Left + Right when firing. And if you try to shoot after losing the gun, your character's arms will rise but no bullets will leave.

Crazy bullets
Go to the left side of the screen, hold Up + Down and then hold Right. As soon as your character begins to move, press Fire. Note: You should be holding the three directions while pressing Fire. The bullets will start from the center of the screen and continue to the right. This is useful if there is a wall in the center and there are robots that you want to hit. Press Left instead of Right when all three directions are held causes bullets to leave from the guy's head.

If this trick is done on the right side of the screen it is sometimes possible to get the bullet to pass through the wall and come out on the left side of the screen.

Go to the right side of the screen, hold Left + Right and then hold Down. When press Fire, the bullet it will suddenly appear on the far left of the screen and not move form that location. If Up is pressed instead of Down, the bullet will appear not as far to the left.