I've been hunting forums and websites for quite a while now, trying to get a clear picture of how defensive attributes (armor, blocking, resists, etc) work in Diablo 3. I've gone through lots of tables, equations, and calculations but I still don't have any good intuition. I've compiled some basic questions/answers to help. Big thanks to everyone who has contributed in this thread!
1) How does armor reduce damage?Armor reduces all incoming damage by a percentage - including elemental damage. This % damage reduction takes place before shield blocking and is based on your total armor and the enemy's level.
2) How do resistances and "resist all" work?Resists work as additional 'armor' to further reduce specific types of damage. These types include Fire, Arcane, Cold, Lightning, Poison, and Physical. Each point in a resistance is equivalent to 10 points in armor, but only works on that particular type of damage. "Resist all" (as the name implies) adds to each of these 6 resistances, providing a very compact collection of defensive boost.
3) How does shield blocking and dodging work?Dodge is a chance to avoid an attack entirely. It works on individual attacks as well as channeled/ground effects. Shield blocking provides a chance to block a fixed amount of damage after it has been reduced by any armor/resistances. Blocking works on individual attacks as well as channeled/ground effects. Shield blocking works while moving (unlike Diablo 2).
4) In what order is damage mitigation applied (first to last)?Dodge
Armor, Reduction Skills (Iron Skin, Blur, etc), Resistance, Barb/Monk 30% reduction
Absorption Skills (Diamond Skin, etc)
5) What kinds of elemental damage do champion/boss modifiers do?Arcane Enchanted = arcane damage
Frozen = cold damage
Molten = fire damage
Plagued = poison damage
Electrified = lightning damage
After further investigation, I believe the following:
Mortar = fire damage (?)
Desecrator = physical damage (?)
Fire Chains = fire damage (?)
I'll be editing this post to add more questions and answers. Feel free to contribute either!
Thank you to: Raesene, Ohlmann, and zakaluka for providing insight. For those who wish to dig into the details, HamletEJ has written a useful blog post on detailed armor mechanics: