Defense Chance at Level

Working page for U14 AC update info.

Armor Class
With Update 14 the DDO combat system was changed from a straight D20 implementation to a more complex calculation. The changes were designed to make Armor more useful and relevant outside the 20 point range of a monsters attack roll.

Our solution is to change the way Attack Bonus and Armor Class are compared. Instead of adding 1d20 to a monster’s Attack Bonus and directly comparing the values, we’re calculating a hit chance separately. Each point of Armor Class increases your chance to be missed, while each point of the monster’s Attack Bonus increases their chance to hit you. The tooltip on your Armor Class value of your character sheet will display your chance to be missed by the “average monster” of your level.

Defense Chance at Level
Defense Chance at Level (DeCAL) is a general indicator of how easy it is to hit your character in combat. Unlike a miss chance, your DeCAL is calculated relative to the average attack roll of a Monster with a CR equal to your character's level.

Note that a 50% DeCAL does not mean that all monsters of your level will only hit you 50% of the time. Monsters vary widely in the abilities: a melee focussed monster will have a higher than average attack roll for its CR while spell uasters will have a lower that average attack roll.

Thread content
The mitigation curve with the live system looks like this. Against a monster with a +20 to hit, if you have a 21 or lower Armor Class (the first red zone), you are hit 95% of the time, since monsters miss on a roll of a natural 1. It doesn’t really matter if you’re at 10 AC, 15, or 21 – you’re still getting hit 95% of the time. At an Armor Class of 40 or higher, once again, each point of Armor Class is excessive – the monster is only hitting on a roll of a Natural 20, so your Armor Class is “wasted”.

Major problems start arising when character AC’s in a party are 20 or more points apart – monsters can barely touch one character but are almost always hitting the other character. The low AC character is taking an astounding nineteen times as many hits as the high AC character. Meanwhile, to challenge the high AC character, monster to-hit numbers have crept up significantly, until we reach our current epic level content, which has charts like this:

Attachment 560 Figure 2: Epic Lord of Blades - Monster attacking Player

The Epic Lord of Blades, without serious debuffs, hits everyone’s Armor Class in the game right now 95% of the time, from the angriest Frenzied Berserker in a loincloth to a Stalwart Defender wearing the best defensive gear in the game.

Since Epic quests, until now, have been designed for a certain extremely hardcore crowd, this was somewhat acceptable, but in Menace of the Underdark we’re opening them up to a wider audience (including Casual, Normal, Hard, and Elite modes).

Players have often told us that the Armor Class system is broken, and the charts above clearly indicate that they’re absolutely right! It’s completely true, especially in high level content. The system functions only in a very narrow band of 20, but player AC ranges wildly from single digits to hovering right around 100. This unsurprisingly leads to characters discarding any attempts to increase their Armor Class, since there’s no way for them to get it to the point where it has any actual effect on gameplay. (Tabletop D&D has a few systems that address the disparity, such as additional attacks per turn at increasing penalties - even if the first attack will hit you 95% of the time, the second or third attack might miss if you have some focus on AC.)

We would like Armor Class to matter to everybody. We would also like everyone to gain some benefit if they acquire an item that increases their Armor Class by another 3 points, regardless of how high their Armor Class already is.

Our solution is to change the way Attack Bonus and Armor Class are compared. Instead of adding 1d20 to a monster’s Attack Bonus and directly comparing the values, we’re calculating a hit chance separately. Each point of Armor Class increases your chance to be missed, while each point of the monster’s Attack Bonus increases their chance to hit you. The tooltip on your Armor Class value of your character sheet will display your chance to be missed by the “average monster” of your level.

Attachment 558 Figure 3: Defense Chance in the AC Tooltip

A general rule with the new formula is that every doubling of Armor Class pretty much doubles your mitigation. A character with 30 Armor Class will be hit approximately half as often by a specific monster as one with a 15 Armor Class, and one with a 60 Armor Class will be hit approximately one quarter as often as the 15 Armor Class character.

Players will use the same formula, but will have a 25% bonus to hit if they are proficient with their weapon. Unlike monster attack rolls, player to hit rolls will be mapped to a d20 by rounding to the nearest 5% - if you hit on a 13, you’ll hit on a 13. Players will also graze opponents on a roll of 2 or higher on the d20 instead of a 10 or higher – if you character looks like it hit with your weapon, it should do some damage on anything but a roll of a 1.

Converting to a system like this increases the band of “Effective Armor Class” dramatically, but also results in high Armor Class characters being hit more often. If we did nothing to address that, the mitigation curves for above charts would look like this:

Attachment 553 Figure 4: Mid Level AC Comparison of Systems – Monster attacking Player

Values from 17 to 305 Armor Class are supported with this mid-level curve. Attachment 554 Figure 5: Epic Lord of Blades Comparison of Systems – Monster attacking Player

The Epic Lord of Blades now acquires a chance to miss at 66 Armor Class, and the curve doesn’t reach a 95% miss chance until 1244 Armor Class.

While these curves dramatically assist characters with Armor Class lower than the Attack Bonuses of their opponents, this isn’t sufficient to keep high Armor Class characters “tanking” as well as we would like. There are two additional changes that we’re planning to help them out there, and one for the lightly armored dexterous classes out there.

More Armor Class for wearing Armor We want armor to mean more to your character than it does today. Currently on live, a character with a 90 Armor Class is likely to be getting 16 or fewer points of their Armor Class from the suit of armor they are physically wearing. We’re creating multiple “tiers” of armor that provide increased bonuses, starting around level 7.

Named items will be retroactively upgraded to grant bonuses appropriate for the tier that they drop at. The Epic Red Dragonplate Armor, for example, will provide 27 total points of Armor Bonus instead of 16.

We didn’t forget about the Warforged – Docents will now also grant different amounts of Armor based on your body feats.

Several feats and enhancements have been modified to provide greater amounts of Armor Class or percentage boosts to Armor Class.

Physical Resistance Rating Heavily armored or defensive characters will be taking decreased damage from physical (bludgeoning, piercing, or slashing) damage due to a Physical Resistance Rating score.

If you are proficient in your armor, you will have a starting Physical Resistance Rating, modified by whether it is light, medium, or heavy armor, that increases as your Base Attack Bonus increases.

Shield Mastery, Improved Shield Mastery, Two Weapon Defense, various Defensive Stances, and the monk’s Earth Stance all provide various amounts of stacking Physical Resistance Rating.

Your Physical Resistance Rating will be visible on your character sheet, and the tooltip will let you know how much it's helping.

Attachment 557 Figure 6: Physical Resistance Rating Tooltip

Dodge Dodge bonuses now give a chance to evade attacks entirely instead of providing Armor Class. Your passive Dodge percentage is capped by the Maximum Dexterity Bonus of your armor, shield, or body feat, but short duration effects can go well beyond it.

Several feats now provide Dodge bonuses that did not have defensive benefits before – Mobility and Spring Attack each grant 2% Dodge, and abilities like Uncanny Dodge and Improved Uncanny Dodge now grant a massive Dodge bonus instead of a small amount of Armor Class.

If we include a 30% Armor Class Boost into our formulas, our Stalwart Defender III tank (wearing heavy armor and a tower shield, with Shield Mastery and Improved Shield Mastery) can expect approximately the following improvement to survivability against the Epic Lord of Blades:

Attachment 555 Figure 7: Includes Physical Resistance Rating and AC increases

Our 100 AC tank on live should be going from 5% mitigation to around 64%. The Physical Resistance Rating boosts give a large amount of durability to the character, and very importantly make a healer’s job easier by making the incoming hits smaller.

In our mid level example, we’ll drop our tank down to Stalwart Defender II (reducing their Physical Resistance Rating), but retain heavy armor and a tower shield. Against this opponent, overall mitigation drops some at high AC values (since it’s no longer really possible to get to 95%), our 40 AC tank on live is still at 78% mitigation overall:

Attachment 556 Figure 8: Includes Physical Resistance Rating and AC increases

Overall Summary: With the new combat formulas, we’re hoping to have Armor Class matter at all levels, for every character. Each point of Armor Class that you gain will help you mitigate damage, whether it’s your 17th point or your 117th. Armors provide increased Armor Class bonuses as well as Physical Resistance Rating. It’s not really possible to reach the 95% plateau anymore, but a high Armor Class character’s survivability will still be high, and the formula is much more forgiving to middling-AC characters.

We hope that this post helps people understand the scope of and the reasons behind the combat changes, as well as providing clarity to make them easier to understand, and we welcome further questions and feedback here in the forums.