The Pre-Martian is the final evolution of the mutants that infest the MPO Mars colony.
When West is found, the Pre-Martian will try to get close to him, throwing out various attacks when it can. The Pre-Martian seems to levitate, so it will randomly take a larger stride, but it is still blocked by the same terrain as West.
At a distance, the Pre-Martian can use two attacks: a red ball and a blue ball. Tossing the red ball causes the Pre-Martian to lunge forward at the same time, but it otherwise has a low range with high damage. The blue ball has a noticeable and significant wind-up, as well as a slow speed; however, when it collides with terrain or West, it explodes violently. The explosion has a large radius and can instantly kill West at higher difficulties, even at full health, if he doesn't have a decent suit. The blue ball will eventually dissipate without exploding if it travels for long enough without hitting anything, but this takes quite a while.
When near melee distance, the Pre-Martian has two more attacks it may use in addition to the above. One is a large radial wave that the Pre-Martian emits from itself; while this does no damage nor contaminates West, it does slow him down temporarily and has a large range. The second attack is a sort of wave of small balls that the Pre-Martian throws out of its torso; like a shotgun shot, each ball does relatively low damage, but being hit by all of them will deal a lot of damage.
Pre-Martians should be among your highest priorities to kill, if not because of their damage, then because they'll be near the front of a crowd that's chasing you. They have a deceptively small hitbox (only its torso can be hit), so a pistol may be useful for its precision and high range (especially useful since even a basic pistol can hit a Pre-Martian before it even attempts to attack), but an SMG may be preferable for its low heat use, despite its inaccuracy. Alternatively, since all of the Pre-Martian's attacks have a noticeable wind-up and it wastes a few seconds between each attack, a brave player can run up to it after it uses an attack and bash at it with a melee weapon or shotgun, running back to a safe distance when it looks like the Pre-Martian is about to attack again.
A fully upgraded pistol can kill a Pre-Martian with a single critical shot (which is common for a fully upgraded pistol) even on Hardcore. In addition, a single Plasma Launcher shot can heavily damage, if not outright kill, a Pre-Martian, which can be useful for heavily infected areas.