Armor was introduced with Zul'jin's patch, but it isn't anything new. It's an all-encompassing term that replaces the old Resistant/Vulnerable system that already existed in the game.
Blizzard has shared some details on the new "armor" system. What do you think about it?
What is Armor?
Armor is an all-encompassing term that we‘re using to replace the Vulnerable/Resistant system that previously existed in the game. If an ability or talent previously referred to Resistant or Vulnerable effects, it will now state that it grants an addition or reduction of “Armor” instead.
How does Armor work?
Armor is split into three types: Armor, Physical Armor, and Spell Armor. Armor by itself means that you gain mitigation from both Physical and Spell damage. Physical and Spell Armor mitigate damage from their respective key words. Currently, all abilities deal Spell Damage while all Basic Attacks deal Physical Damage (with slight exceptions like the talent Cannoneer, which turns Li Ming’s next Basic Attack into Spell Damage). For reference, floating damage text will display Spell Damage as purple numbers above the target’s head, while Physical Damage will display as orange.
As of the Varian patch, abilities and talents that grant Armor now stack additively. There were a lot of ways that we could have designed this, but in order to keep the system as simple as possible, we decided to make each point of Armor directly relate into 1% resistance. Technically, this means that each additional point of armor is slightly more valuable than the last, and in order to keep that in check we created lower and upper Armor Caps of -25 and +75, respectively. The reasoning and thoughts behind doing this were outlined by Matthew Cooper in this post.
Exceptions and Interactions
You will notice that there are a couple of talents that can raise or lower Armor past their respective caps. Things such as Nazeebo’s Superstition (-30 Physical Armor) or Arthas’ Anti-Magic Shell (+100 Spell Armor) are specifically flagged to ignore the caps, but function identically to the rest of the system. Abilities that ignore Armor Cap are currently rare, but in the future we may implement more abilities and talents that bend the rules. In the case that two different effects are both ignoring the Armor Cap, the larger one will take priority.
As an example, let’s say you are playing Nazeebo and picked up Superstition (-30 Physical Armor, +50 Spell Armor) and then receive a Pixie Dust (2 stacks of +75 Physical Armor) from Brightwing. You would now currently have 45 Physical Armor (-30 + 75 = 45) against the next two Physical damage sources.
Again, let’s say you have Superstition (-30 Physical Armor) and are hit by Tyrande’s Hunter’s Mark (-25 Armor). You would now have -30 Physical Armor (already at/past Armor Cap) and 25 Spell Armor (50 – 25 = 25).
Percentage based damage is now flagged to ignore the Armor system entirely. This means that your Giant Killer (+1.5% Max health damage per attack) will do full damage to your target regardless of their current Armor state.
We realize that you will definitely have more questions about this system and are doing our best to make it as clear and transparent as possible. We are currently working on several ways to better explain the system to players both in and out of game, and are actively listening to your suggestions and feedback. While this might seem like a big change, rest assured that the balance team is patiently watching the state of the game and are ready to make any changes necessary to keep the game as balanced and polished as possible as we continue to roll this new system out.