Iron Man has created plenty of interesting and unique armors for himself in Marvel Comics as well an in the MCU films. It seems like he has an armor for any given situation. However, one such armor from the comics is notably unique. Not just in its particularly dark purpose, but also in the material its made from. Known as the Cold Iron Armor, this suit allows Tony Stark to take on a very specific enemy: Malekith, Lord of the Dark Elves, and all of his elven forces. Read on to learn why it's such a unique and intense armor.
While Malekith is typically a nemesis of the Thor, the God of Thunder, Iron Man sets his sights on the dark elf after the villain gets his hands on a few Mandarin rings. Initially meant to be a stealth mission on the dark elves' realm of Svartalfheim to retrieve the rings, Tony Stark is discovered and Malekith sends his dark elves to hunt Iron Man down. He gives each of his captains a Mandarin ring, supposedly to help them kill Tony once they've tracked him. However, Iron Man is never without a backup and contingency plan, usually in the form of a new tech or armor. In this case, one very deadly armor.
Apparently, a fighting-fire-with-fire approach is needed when facing the dark elves. Tony calls Dark Angel, a tech/magic expert assisting him, to send him a brand new armor, known as the Cold Iron armor. While most of Iron Man's suits are not actually made of iron (as he mentions in the first Iron Man film), this particular suit is. The reason for the iron used is that the metal is found to be lethal to dark elves. Upon contact, the elves experience an excruciating pain and burning cold, hence the armor's name. With his new suit, Iron Man turns the tables on those elves hunting him, making them the prey.
This suit is arguably more intense and more "metal" than any of Tony's other suits. Featuring long iron claws on each gauntlet for piercing, and a launching harpoon attached to the shoulder, it also fires clouds of iron filings, ensuring little chance for any elf to escape the inevitable freezing burn. Iron Man isn't messing around wearing this suit. Why should he, considering that Malekith would like nothing more than to flay him alive? However, the armor and its dark purpose also seem to come with an even darker disposition for Tony himself. He seems less forgiving and more merciless than normal, filled with anger towards Malekith and his forces.
One could imagine how different the Thor: The Dark World film would have been had Iron Man been present to help Thor fight the MCU version of Malekith, especially if Tony wore this armor. It probably would have been a much shorter movie (something that Dark World might have benefitted from). In any case, it's probably a good thing Iron Man only briefly used this armor. While useful, it's lethal and intense applications are probably better suited as a one-off suit, rather than some of his more long-standing consistently worn armors.
At the end of the day, Iron Man is at his best when he's a more lighthearted hero, rather than being one filled with vengeance.