Iron Skin was a Barbarian passive skill in early versions of Diablo III. It worked exactly as it did in the second game: toughened the Barbarian's skin, increasing armor by X%. With the change of skill tree design, it was replaced with skills like Ignore Pain, Tough as Nails and Nerves of Steel. With the introduction of Reaper of Souls, the skill of the same name has been added to the Crusader class.