Alien 3

The shield wall is indestructible, but the robots and the cannons aren't.

They'll go from side to side of the screen in an alternate movement shooting down.

Three high density molecular laser shields are placed in defense of the laser cannon.

Each one of them houses an extra cannon.

Instead of a passing flying saucer as seen in Space Invaders , the Merciless Monstroth moves left and right at the top, shooting down at the player.

The player controls a robot defender inside the laser cannon.

If the laser cannon is destroyed, the robot will be left unprotected.

The robot can enter a new laser cannon housed in one of the shields.

Once the new laser cannon is active, the shield is gone.

Once the three shields are gone, the Merciless Monstroth will come down to hunt the player's cannon and robot.

The player wins a battle when destroying all enemy robots and cannons on the screen.

A battle is lost when the player's robot is destroyed.

The first side to win ten battles wins the war.