This walkthrough will help you earn an S Rank score in the Root Cause story mission in Metal Gear Solid 5: The Phantom Pain, and includes a list of the mandatory and optional objectives available for this mission. Keep in mind that it is not necessary to complete all the optional objectives to earn an S Rank. All you need is an accumulated score of 130,000 or more, and completing the mission quickly can often grant you an S Rank from the time bonus alone, which we will show you here.
- Extract the Intel Team member (Mandatory).
- Extract the Intel Team member before he is involved in an accident (Optional).
- Exfiltrate the hot zone with the Intel Team member by land (Optional).
Hop on D-Horse at the start of the mission, and ride forward toward a nearby road. Continue riding uphill along the path, making your way around the back side of the nearest outpost.
As you approach the outpost, look for a guard near a sandbag barricade and take him out with your tranquilizer pistol. Afterwards, locate the Intel Team member wandering somewhere near the back of a truck near the sandbags.
Pick up the team member and carry him to the truck in front of you, placing him in the passenger side. Now, all you have to do is hop in the driver’s seat and drive up the hill to leave the area. Once you have cleared the hot zone, the mission concludes. Completing the mission in just under two minutes should easily secure you an S Rank score from the time bonus alone.