Dark Armor is a Scrapper secondary powerset in City of Heroes as well as a Brute and Stalker secondary powerset in City of Villains, and as of Issue 12 a Tanker primary powerset in City of Heroes.
Dark Armor allows you to tap into the powers of the Netherworld for protection. Many Dark Armor powers drain your foes to strengthen you. Dark Armor offers very good resistance to Negative Energy damage, and is one of the only defensive sets that offer some resistance to Psionic damage. However, its resistance to Energy is weak and it offers no protection to Knockback.
A shroud of Netherworld darkness envelops you, making you difficult to spot at a distance. You can be seen only at close range, or if you attack a target. Even if seen, the Cloak of Darkness grants you a bonus to Defense to all attacks and some protection from Immobilization. This Netherworld Cloak also allows you to see things in a new light, allowing you to better see Stealthy foes. Unlike some Stealth powers, Cloak of Darkness has no movement penalty. Cloak of Darkness will not work with any other form of concealment power such as Shadow Fall or Steamy Mist.
You can wrap yourself in a nightmarish Cloak of Fear. Foes close to you are treated to visions most horrific, forcing them to tremble in terror, only attacking if attacked, and even then, with a reduced chance to hit.
Hide makes you almost impossible to detect. When properly 'Hidden', a Stalker can pull off Critical Hits with his attacks, and even land a massive 'Assassin's Strike' with an assassin's power. When you attack or are damaged while using this power, you will be discovered. Even if discovered, you are hard to see and retain some bonus to Defense. Unlike most Stealth powers, Hide can be used at the same time as other concealment powers, giving you even greater Stealth capability.
The Netherworld has many mutable properties, such as the Oppressive Gloom. This power allows you to use your own Hit Points to keep enemies near you Disoriented and unable to use any powers. Endurance cost for this is minimal, but the power can be dangerous to use.
You are a true Shadow Dweller of the Netherworld. Your affinity for the shadows grants you an inherent bonus to all Defense, as well as an increased perception and a resistance to Immobilization. Your perception bonus and resistance to Immobilization improves over level. Shadow Dweller is an auto power. It is always on and costs no Endurance.
Should you fall in battle, you can perform a Soul Transfer, sucking the life force of all foes around you to bring yourself back from the brink of death. The more foes nearby, the more life is restored to you. Drained foes are left Disoriented. The dark effects of this Soul Transfer will actually leave you invulnerable for a brief time, and protected from XP Debt for 20 seconds. There must be at least one foe nearby to fuel the transfer and revive yourself.