How to beat Rex in Metal Gear Solid (MGS Metal Gear Rex fight)

In the Metal Gear Rex battle, start by equipping the Body Armor, then throw a Chaff Grenade so Rex cannot lock onto you.

To damage Rex, target the radome on its left shoulder using the Stinger.

Repeat this - keep moving, throwing Chaff Grenades and firing at the radome - until Rex's health is fully depleted.

If you run out of items, they spawn along the sides of the area. For example, Chaff Grenades spawn on the right side, in the middle.

In the second half of the battle, stay underneath Rex until the radar is blue. When it's safe, fire a Stinger at the cockpit. From beneath is fine - even without locking on first!

Repeat this process - running underneath, firing up at the cockpit - to defeat Rex for good.