In Update 14 there were dramatic changes to the way armor class works in DDO. I’m going to try and explain how it works and more importantly how you can use the new system to your advantage.

Lets define some terms

• Physical Defense: Anything that protects you from attacks by weapons.
• There are now five types of physical defenses in DDO
  • Damage Reduction: This defense reduces damage you take by a fixed number. It does not generally stack and there is often a means to bypass it by the use of special damage types.
  • Physical Resistance: Is like damage reduction but instead of a fixed number it reduced damage by a percentage.
  • Miss Chance: This is a percentage chance that a monster will miss you with an attack. Three common types of miss chance are Dodge, Concealment, and Incorporeal states.
  • Fortification: This is a percentage chance to avoid taking critical hits.
  • Armor Class: Armor class represents how difficult it is for you to be hit. When you attack you must overcome your opponents armor class on your attack roll to land a hit.

When you are attacked, this is what happens:

1. First you check miss chances: Each type is checked separately. If the attacker rolls below the miss chance they may continue the attack, otherwise the attack ends.
2. The attacker makes an attack roll which is compared to armor class
3. If the attack roll is higher than your armor class you are hit
4. If the attack roll is not higher but is within a certain range, you take a grazing hit
5. If there is a hit or grazing hit the attacker rolls damage (grazing hits do far less damage)
6. If the attack is a critical hit, fortification is checked. If the attacker rolls over the fortification value, damage is multiplied by the attackers crit multiplier.
7. Next up the damage is reduced by the Physical Resistance lowering it by a percentage.
8. Finally any damage reduction that is not bypassed by the damage type is applied reducing the incoming damage by a fixed amount.

Attack vs Armor Class in Detail

Armor class is the most complicated of the defense types. In classic D&D if your attack roll is a larger number than your target’s armor class you hit. Because you roll a Twenty Sided dice in D&D there is a window in which a change in armor class or attack will matter. If you have a +40 to hit there is an AC window from 42 to 58 where adding or losing AC will make a difference. Anything outside of that is either a near automatic hit or automatic miss. A roll of 1 is always a miss and a 20 is always a hit so it’s never impossible or completely automatic.

In DDO this caused problems because there were so many ways to raise AC and attack values that the windows were much smaller than the possible character values. This led to AC becoming either something you hyper specialized in, or something you completely ignored. It made things very hard for the developers to balance well.

The new system is quite a bit more complicated. A 1 is still always a miss, and a 20 is still always a hit, that part remains unchanged. But how you roll to hit is rather different. There is now a formula that gives you a percentage chance to hit:

(To-Hit+10.5) / (2*AC) +.25
(players only and only if proficient with weapon)

If you and a monster are roughly equal, you will have a 75% chance to hit them, and they will have a 50% chance to hit you.

When you roll your d20 the system rounds the % value into a 1-20 with 1 being 5% and 20 being 100%. 19 is 95%. This way you can still roll a d20 to see if you hit but under the hood it’s no longer a linear relationship.

As to-hit rises above AC the chance to hit increases fairly rapidly, but as AC exceeds attack the chance to hit decreases in a bell shaped curve, steeply at first but then ever more gradual. Each point of AC gives a bit less of a benefit from the last one. Also as you the numbers overall get larger, the effect of each point of attack and AC diminishes so the “window” from hit on a 2 to miss on a 19 gets larger and larger.

The result of all this is that its harder for you to get your AC up to where you almost never get hit, but it is much easier to get it to where you will get hit only 30% of the time. The higher level you are, the more remote the extremes are.

Lesson to take away

1. Increasing your armor class will generally benefit you with getting hit less often until your AC gets well above the attack of the monsters you are fighting. If you can get more AC on your character it is probably worth doing so, but if your AC is already high and you would have to make a sacrifice in some other area to get more AC, it likely isn’t worth while.
2.  Hitting monsters is incredibly easy now and sacrificing accuracy for AC or accuracy for damage is almost always a good trade off. With a half-way decent attack score you will only rarely miss except on a 1.

So how do you get more AC?

An exhaustive list could take hours. AC can be had from numerous sources and the rules about what AC bonuses stack and what ones don’t can be complicated.

Every character starts at a 10AC baseline and this value is then modified up and down by various effects.

Armor 101

The most classic source of AC is Armor, indeed this is the origin of the term. What armor you wore in the original D&D determined what your Armor Class was. In DDO it is but one of many sources, but it is often the largest for most armor wearing characters.

There are three important stats on armor that determine its AC benefit. First is its Armor Bonus which is its base AC value, second is its enhancement bonus which is added to the Armor Bonus. Finally there is Max Dex Bonus. This tells you how much of your dexterity bonus you can add to your AC while wearing the armor. It also sets the maximum amount of dodge you can benefit from. Any value bigger than your actual dex bonus or dodge value is not going to help you.

Armor comes in three categories: Light, Medium, and Heavy. Light armors give the least AC and heavy armors give the most, while max dex is the reverse with light armors offering the most and heavy armors the least.

Each weight of armor has two types, for instance leather and chain are the two types of light armor, scale and breast plate are medium, while half plate and full plate are the heavy armors. In each category one of the armors will have a higher AC rating while the other will have a higher max dex value.

Furthermore each armor weight also comes in 5 different ranks based on a stat called absolute minimum level. The base rank starts at level 1 and goes up to 3, the second rank is from 4 to 9, the third from 10-15, the fourth from 16-21 and the fifth from 22 to 25. (shields have slightly different level breaks)
The higher the rank the more armor it provides.

Of course not every character can wear any armor they like. Arcane casters can suffer from arcane spell failure in most armors and characters cannot benefit from evasion wearing medium or heavy armor. That and armor proficiencies may limit your choices. Wearing armor you are not proficient in will incur a hefty attack penalty equal to the armors armor check penalty so that may also be a limiting factor.

Docents

Warforged body types and docents are now a bit different too. Docents don’t have types or categories, but they do have the 5 ranks just like armors do based on absolute minimum level.

The body types determine max dex rather than the docents themselves and they also determine the effective weight of the armor. Adamantine body is treated as heavy armor for all intents and purposes. Mithral is considered light armor except that the protection it provides is closer to traditional medium armor. Composite provides protection about like light armor, but it is actually treated as not being armor at all for class abilities and so forth.

Legacy armor

Random loot armor that was in the game prior to update 14 is legacy armor and is always the lowest rank of armor no matter its minimum level. At low level it is still comparable but at high level it is almost always worse than the new armors. Most named armor was upgraded and doesn’t have this problem.

Legacy armor can also come with the mithral and adamantine metal properties. Mithral used to be very valuable because it increased max dex values, but now it is only found on legacy armors which are always the lowest rank. Thus they are only meaningful for low level characters any more. Named armors still may have these properties and they work fine there, but otherwise they are no longer relevant.

Armor Take Away

• Don’t wear armor that interferes with your class abilities
• Wear armor with a minimum level close to your character’s level
• Wear armor with a high enhancement bonus
• Wear armor with a max dex bonus that is as close as possible to your dexterity/dodge bonus

Shields

Shields are very much like armor. There are different types of shields (buckler, light, medium, and tower) as well as 5 ranks based on absolute minimum level. And they also have enhancement bonuses. The heavier the type and the higher the rank and the bigger the enhancement bonus the more AC they will provide.

Tower shields are the only type that has a maximum dex value and thus the only type that can restrict your AC bonus from dexterity.

Also like armor, shields can create arcane spell failure for some classes and not everyone is proficient with all types of shields and using one without proficiency can give you attack penalties.

Unlike armor, using a shield can negatively impact your damage output by disabling two weapon fighting and two handed fighting. Still, if you want to maximize AC, a shield is often a must have item and the two best prestige enhancement lines for defensive characters gain extra benefit from using shields. Remember that defenses only matter if you are getting attacked a lot. That means either solo/small group play or if you are a party tank. Otherwise maximizing your DPS is likely going to benefit your group more than our turtling up.

Tank type characters have to balance defenses and offense because agro is based largely on the damage you deal and the agro amplification you have. Shield mastery helps a little with damage output and shields with +10 seeker on them are also a nice bonus, but your best bet is to crank up on the threat amplification through items, class abilities and the intimidate skill.

Crafting armor and shields

When crafting armor and shields you want to break down an item of the rank you want to end up with. Too high and you can’t use it, too low and you won’t get the maximum armor value. Armor blanks made before update 14 is always the lowest rank and therefore likely not of much value to you any more.

AC bonus types from other items and spells

AC bonuses from other items come in a range of types. Deflection is a common type that comes from the shield of faith spell, protection items, and various other sources. Natural armor is another common AC bonus that comes from barkskin and various items. There are also sacred, profane, alchemical and other AC bonus types. Generally they don’t stack if they are of the same type but there are exceptions which are usually toned in the item or spell description.

Anyone serious about AC will be looking to get at least a 5 natural armor and 5 deflection bonus to AC and as much of the others as you can muster.

AC bonuses from character abilities

A number of DDO character classes, enhancements, feats, racial abilities and so on can contribute to your armor class. Most class based ac bonuses will stack with whatever gear and spells you may have unless they are spell like powers. Of the lot, the Fighter’s Stalwart Defender and Paladin’s Defender of Siberys offer the biggest defensive bonuses. Stalwart is very focused on armor use, while Sybaris is less so. Monks also have some AC bonuses to offer but they all are dependent on not using any armor or shield. While other classes do have something to offer in the AC arena, none can match these three.

Miss chance and dodge

Let’s quickly talk about miss chances. Dodge is the new kid on the block here. It used to be that dodge was an AC bonus that was unique in that it always stacked. In the new system each point of dodge is a 1% miss chance. Its also capped by the max dex of your armor and has an absolute maximum of 25%. Rogues and Barbarians receive dodge from their uncanny dodge ability now, and monks can get some dodge bonuses from water stance. The Dodge, Mobility and Spring attack feats also grant a few points as do all the old equipment items that used to have AC dodge bonuses. Its not easy to cap it out at 25% but it is possible. That said most armor wearing characters will have a lower limit. There are also some short term boosts that can take it above the normal maximums.

There are also concealment and incorporeal miss chances. Each type is checked separately so some of each is great, but bonuses of the same type don’t stack. The displacement spell is the best concealment bonus at 50% but can be bypassed with true seeing. Displacement is self cast only, but you could UMD scrolls, or even take the elven dragonmarks to get it on a non-caster. Incorporeal is very rare, only found in Ninja Assassin, Shadowdancer, and Pale master and is bypassed with ghost touch which is rarely found on monsters.

Miss Chance Take away

Take any opportunity to get some miss chances for your character of each type you can. Dodge can be the most work to get and the least rewarding but don’t turn your nose up at it. At higher levels each point of AC will have less impact but each point of dodge is always worth +1% defense.

Physical resistance rating

Physical resistance is another entirely new mechanic. It reduces the amount of damage you take from physical attacks by a percentage. The PRR value is not the percentage of reduction. Like armor class it has a kind of diminishing returns system. The formula is

1 – (.99^PRR) x .65

The upshot of this is each point of PRR you have is worth a bit less than the last. At around 50 PRR you are getting about half the rating in reduction 26%. From there it gets a bit worse and you will need to reach 150 PRR before you can reduce damage by half.

Because its a percentage system, at low level you often will only be reducing damage by a point or two, but at high level you get harder and the reduction will be a larger absolute number.

PRR comes from a few sources. Armor grants some PRR based on the weight of the armor and your character’s base attack bonus. Heavier armors give more than lighter ones. There are also a number of prestige enhancements and epic destinies that grant some PRR with the defender lines being the stand-outs. Shields don’t grant PRR directly but in combination with the shield mastery feats and some of the prestige enhancements they can contribute a good chunk.

Damage reduction

This hasn’t changed much from days of old. It effectively stacks with PRR though the mechanic is very different. DR simply reduces the physical damage you take by a set amount. While there is no way to get around PRR, most DR can be bypassed with certain damage types such as silver, adamantane, magic, blunt and so on. DR will always list what types of damage bypass its effect. DR pretty much never stacks but if they bypass one source it won’t always bypass all of them so there can be a reason to have more than one source of it.

Grand summation

1. Every character can benefit from defenses now so its squeeze it in wherever you can without sacrificing the primary mission for your character.
2. If you are dedicated to good defenses you want to get as many different sources as you can. AC and PRR offer diminishing returns so if you have to choose, shore up your weakest defenses first.
3. Against physical attacks heavy armors are generally better since they offer both AC and PRR and don’t need much investment in character dexterity.
4. If you are currently using non-named armors and shields from before update 14, junk them and look for new ones. Avoid legacy armors on the auction house.
5. If you want to be a real tank, go paladin, fighter, or possibly monk. Combinations of those with other things work as well.

Related Episode:  DDOCast 258