During Mission 2: Through the Eyes of Evil (Training Mission), you will be asked to complete some very easy tasks during basic training. At the end, you will be asked to run an obstacle course, and after deductions your time must be 18.0 seconds or less. Before starting the course, switch to single shot (down on d-pad) and switch to iron sights for aiming. Run the course a few times and memorize the patterns, and aim for headshots. Eventually, you should be able to run the course very fast without reloading and getting mostly headshots. You will get 30 second of deductions if you get all 16 enemies with headshots.
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