Rockbreaker

The Rockbreaker is a category of machine in Horizon Zero Dawn. A large Acquisition Class machine, the Rockbreaker is unique in which it is the only known machine capable of subterranean ambulation. It was designed and developed by the AI GAIA for the mining of underground minerals. However, after the Derangement, the Rockbreaker is a large, lethal threat to any human who walks on the ground above it.

History
Rockbreakers were presumably created by the Zero Dawn terraforming system’s governing artificial intelligence (AI) GAIA as one of the machines designed for terraforming the Earth after it was left lifeless and sterile by the Faro Plague in the mid 21st century. However, after GAIA self-destructed, the AI HEPHAESTUS, formerly a subordinate function that manufactured machines under GAIA’s direction, gained control of four Zero Dawn cauldrons and the machines they produced It altered the behaviour of Rockbreakers and other machines from docility to hostility, becoming so aggressive that they attack humans on sight.

Appearance
A Rockbreaker’s chassis closely resembles the body of badger or a mole, though unlike these animals, it has a tail whose length is approximately one quarter of the length of its body. Its most prominent feature is a massive mouth, composed of an enormous roller-cone drill bit. Each cone is set in a hinged jaw. This configuration allows the bit, and therefore the mouth, to expand as needed. Twin optical sensor arrays are located in the same position on the head as a mole’s eyes. However, while a mole has very poor eyesight, a Rockbreaker’s optical sensors are fully functional. At the end of each of its four short, stout, powerful limbs is a large extremity called a digging arm that resembles an excavator’s shovel. Under the machine's belly are twin Blaze sacs, and twin exhaust ports are positioned atop the body at the base of the tail.

Behaviour
The Rockbreaker is built for underground mining operations, tunneling through rock and soil with its mouth, ingesting large quantities of rock, which it processes and extracts mineral resources from. It surfaces frequently to expel large boulders, presumably boulders of processed rock, from its mouth. During activity, it may form a mound of rubble on the surface containing resources that humans find useful. At intervals it rests on the surface for a short time, presumably to release accumulated exhaust, before descending underground again. Like all large machines, Rockbreakers are never found in groups of more than two. The mineral resources that it extracts are presumably collected for transport to cauldrons to manufacture new machine units.

Abilities
A Rockbreaker’s most formidable ability is its subterranean capacity; it can emerge from the ground, attack, then immediately return underground to emerge and attack at another position entirely. This ability works in tandem with the speed at which it ambulates underground; a Rockbreaker “swims” through the ground below the surface with the ease of a shark swimming underwater. Thus it can repeatedly emerge, attack, return underground and change position at very high speed. The only indication of its location is the dust trail and rumbling sound that the ground produces when the machine is moving near the surface. Furthermore, the Rockbreaker’s subterranean ability makes putting it into an elemental state difficult, as it prevents the repeated strikes from elemental weapons needed to cause such a state. This is also the case with tying it down; by going underground, the Rockbreaker breaks any attacked Ropecaster lines before full tie-down is achieved.

Rockbreakers are sensitive to sound. If a human walks or runs on ground under which a Rockbreaker is present, it will zero in on the sound and attack. If a projectile or energy weapon is fired, the Rockbreaker immediately zeroes in, not on the sound of the projectile or energy bolt striking, but on the sound of the weapon being fired. This includes the relatively quiet sound of a bow release.

Rockbreakers mainly employ melee attacks, most of which utilize its ability to emerge on the surface at high speed. However they can also ambulate on the surface with surprising speed, and are actually capable of overtaking an athletic human at full run. Additionally they employ a ranged attack in which they hurl boulders from their mouths at an enemy.