The Giant Death Robot is the only unit in Civilization V to be fictional (apart from the Landships and Airships featured in the included Gods and Kings steampunk scenario "Empire of Smoky Skies ") However, the Civilopedia mentions that it is possible that the mech is being developed secretly by governments.
The Giant Death Robot is a powerful unit when attacking. However, it is weak when defending, so don't leave it on its own. You also don't want to stack defensive bonuses on it. The best thing to do is to make them attack, then move them away to the back of your army.
Receives penalties when attacking Cities and on defense, but is otherwise stronger than any other military unit in the game.
The "mech" is a giant bipedal mechanical robot armed with a variety of missiles, gatling gun arms, laser-beam eyes, and a deadly kung-fu punch. Although not currently found on the modern battlefield, no doubt across the world governments and evil corporations are secretly developing these metal behemoths even as we speak. When these mechs come into service, all of the world's other weaponry will become obsolete, and humanity's fate will be decided by a climactic battle between armies of good and evil mechs in the streets of downtown Tokyo. (Assuming that the giant radioactive monsters don't get us first.)
- The Giant Death Robot may be a homage to the assault mech in Next War, a mod included in the Civilization IV expansion Beyond the Sword. The assault mech in question was featured on BTS's box cover. The unit or at least its name may also be derived from this thread by user Perfection in the Civilization Fanatics Center.
- It could also be considered a homage to the mech REX from the Metal Gear Solid series, due to the information inside the Civpedia: Gattling Guns, Laser-Beam eyes and close-range melee fighting all being part of REX's arsenal, especially with the "goverment and evil corporations" developing them.