You’ll face the Metal Gear Sahelanthropus in mission 31 of Metal Gear Solid V: The Phantom Pain. It’s not a very pleasant fight, so be sure to bring in your best grenade launcher and rocket launcher. You’ll also want to bring a fast-firing lethal pistol with you as it’ll come in handy towards the end of the fight.
Right at the start of the fight, fire your rockets at the Metal Gear’s torso, where all the white tubes are. You can fire at both the front and back of the torso. At the same time, Kaz and Ocelot will continuously call in the support chopper to provide backup fire. However, if the Sahelanthropus manages to destroy the chopper, you’ll have to manually call it in from the iDroid if you want the air support to continue. Kaz and Ocelot will also automatically call in supply drops each time you run out of ammo for a weapon, so if you don’t have a lot of GMP, expect it to go into the red during the course of the fight.
Aside from using you own weapons, you can also hop into one of the tanks lying around the area to do some damage. If you’re skilled enough with maneuvering a tank, you can easily shoot the Sahelanthropus while staying on the move.
The Sahelanthropus has quite a few attacks you’ll have to watch out for as well. When it strikes the ground with its whip, Big Boss will be surrounded by tall, dark rocks. The best way to deal with this attack is to stand still in the middle of the rocks; coming into contact with them will cause the rocks to explode and cause some serious damage to you. After awhile, the Sahelanthropus will blow them up, leaving you free to run out of harm’s way once again.
The Sahelanthropus can also fire guided missiles to your position, but this isn’t really a big deal as you can easily run out of the danger zone. However, when you see the Sahelanthropus leap into the air, quickly look around to determine it position and run towards it. It’ll usually be standing atop a tall cliff and getting ready to fire a huge laser beam at your position. Run towards it and take cover at the base of whichever cliff it’s standing on to avoid getting hit by the beam. One hit from the beam will kill you instantly so it’s better to take cover at the base of the cliff until the Sahelanthropus leaps off again.
Once you have the Sahelanthropus down to about a quarter of its health bar, you’ll occasionally go into Reflex Mode and get a glimpse of the Psycho Kid leaping into your sight. When this happens, quickly equip your pistol, or any other fast-firing weapon to hit him. This will incapacitate the Sahelanthropus, allowing you to fire two free rockets at it before it gets back up again.
The fight will end once you’ve depleted the Metal Gear’s entire health bar, and you’ll also receive a big GMP reward as a result of completing the mission. Beating the Sahelanthropus will mark the end of the first chapter of the game.