Compared to other anime mecha, Gundams are built more like actual machines of war, with an emphasis on practical, clear designs. However, the following Gundams are not merely weapons of war, but weapons of terror as well. The following six Mobile Suits were built to inspire fear in those who see them.
GFAS-X1 Destroy Gundam (Mobile Suit Gundam SEED Destiny)
Being three times the size of a normal Mobile Suit, Destroy Gundam is designed to inflict as much damage as physically possible as fast as possible. It sports two modes: a gigantic imposing mobile suit and a saucer-shaped gigantic cannon. If you are staring down the barrel of this monster, you have nowhere to hide.
Destroy Gundam is intimidating from a distance, but it's slow and clumsy enough to be vulnerable to close-up attacks. However, when it turns an entire landmass into a massive inferno, Destroy Gundam lives up to its name.
XXXG-01D2 Gundam Deathscythe Hell (Mobile Suit Gundam Wing)
Duo Maxwell is one of the heroes of Gundam Wing, yet he pilots one of the most nightmarish and ghoulish Gundams ever conceived. The upgraded version of the Deathscythe Hell is one of the edgiest Gundams ever, looking more like a mechanized demon than a machine of war.
Wielding gargantuan wings and a killer scythe, this demonic-looking machine is designed to strike fear into the hearts of its enemies. However, what makes the Deathscythe Hell arguably more terrifying of all is, due to being designed for stealth missions, it has the troubling ability to camouflage itself. It can go invisible, sneak up behind you and then slice you apart with its scythe.
GNW-003 Gundam Throne Drei (Mobile Suit Gundam 00)
What if a Gundam had a xenomorph head? This question was answered by Gundam 00's Gundam Throne Drei, one of Celestial Being's second team of Gundam fighters. Piloted by Nena Trinity, Gundam Throne Drei is a stealth unit designed to inflict maximum damage with minimal engagement.
What makes this Gundam so terrible to fight is its Stealth Field. It can disrupt all forms of radar and location over a wider range than any prior Stealth Field could muster. Add to that a long-range rifle, and anyone is toast facing Nena. The design makes it look downright.
MRX-010 Psycho Gundam Mk-II (Mobile Suit Zeta Gundam)
One of the oldest Gundams on this list, the Psycho Gundam Mk-II is an improvement over the MRX-009 Psycho Gundam, which itself probably could have qualified for this list. The prior model was a titanic mountain of metal and power, easily able to overpower those who stood in its way. However, the Mk-II is vastly more powerful, containing far more fire-power and energy-efficient manners of attack.
However, the Psycho Gundam has one added element that makes it somewhat even more nightmarish. So long as its head remains intact, it can be rebuilt, stronger than before. Even when it is taken down -- sometimes at a great cost -- it can return so long as its detachable head flies off. That is a nightmarish image in and of itself.
JDG-00X Devil Gundam (Mobile Fighter G Gundam)
The Big Bad of Mobile Fighter G Gundam, the Devil Gundam was originally created to be the "Ultimate Gundam," an integration of biotechnology and machinery. What no one could have predicted is that the Ultimate Gundam project would be sabotaged by selfish monsters, resulting in it becoming a rogue agent. Much like many rogue AIs, the Devil Gundam concluded that the only way to save the planet was to eradicate humanity. Thus the Devil Gundam underwent a series of self-replications, ultimately becoming an entire space colony capable of eradicating the nations of the world.
What makes the Devil Gundam terrifying, aside from its colossal and demonic appearance, is that it spreads DG Cells, a cellular compound designed initially to cure all diseases. However, the Devil Gundam chose instead to make these drive people into fits of rage, turning them into agents of its will. Oh, and to make matters more terrifying, the Devil Gundam uses human beings as power supplies, regardless of if the individual is willing or not to use the host. The Devil Gundam is the closest thing to a cosmic-level threat in all of Gundam.
Angel Halo (Mobile Suit Victory Gundam)
Is this cheating? The Angel Halo is less a Gundam and more a gigantic weapon used by the Zanscare Empire. However, it remains one of the most bone-chilling instruments of war in the entire Gundam franchise. By harnessing the power of 2000 comatose "psychochickers," the Angel Halo generates "psycho waves" to artificially regress the human mind, reducing a whole planet's population to descend into a comatose state. Prolonged exposure will cause cellular degeneration and complete decay.
If that sounds nightmarish, it isn't even as terrible as an earlier model of the Angel Halo, which, rather than create waves, would just unleash a deadly virus. That idea was discontinued when they couldn't figure out how to cure the virus. The Angel Halo is an instrument of war too terrifying not to include on this list.