Instructions
Select as high a difficulty as you can handle. Recruit difficulty offers the normal amount of points during gameplay and each subsequent difficulty provides twice the points.
Select skulls when setting up the game. These are optional modifications to the normal gameplay. For example, you can set one skull to change how the enemy fires or change how lucky they are in firing projectiles at you. These will include bonuses to your points.
Defeat enemies to score points. Take cover to avoid enemy fire and aim for the head to quickly dispose of your opponents.
Destroy enemy vehicles. In later waves, enemies will try to run you over with large vehicles. Destroying them results in bonus points.
Survive. Above all else, surviving as long as you can will allow you to rack up the greatest amount of points.