Introduction to Mechanics Guide

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General Mechanics Guide


WDM stands for Weapon Damage Multiplier. Put simply this is a % modifier of damage done. If you would do 1,000 damage, and your skill has 50% WDM, then you do 500 Damage before further reductions.

► Calculating Weapon Damage

Next Delay
Just about every non melee attack in the game uses Diablo's "Missiles" system. An arrow, a spell, anything that isn't a melee "slap" carries a stat called next delay (ND for short). The ND number is the amount of frames a missile has to wait before hitting again. If a piercing missile has 0 ND, it can hit every single frame it is currently passing through an enemy's or player's hit box. If a piercing missile has 1 ND, it hits every other frame, 2 ND is every 3rd frame, and so on. Since the engine runs at 25 frames per second, a single piercing missile with 0 ND (and a big enough hit box/slow enough movement) could hit 25 times a second on an enemy.

Life and Mana Leech get reduced a higher amount in higher difficulties, and then again vs bosses in each difficulty.
Normal Effecitiveness : 1/4 th.
Nightmare Effectiveness : 1/7th.
Hell Effectiveness : 1/15th.
Bosses have a 40% reduction to leech in all difficulties.

Crushing Blow
Reduces an enemies current HP by %.
1/4 vs enemies while attacking them in melee, 1/8th with ranged
In Sigma Bosses are completely immune to crushing blow.

Deadly Strike
Flat % chance of doubling physical damage on the attack on success, this is calculated before conversion.

A WDM skill can carry conversion. This takes a stated % of your damage you would deal, and then shifts it to whichever element is stated. This is not amplified by spell damage, but it does take pierce into account.

Reducing Incoming WDM damage

DEFENSE: Most WDM attacks first have to pass the defense check, it uses the following formula:
Chance to be Hit = 100 * AR / (AR + Defense ) * 2 * attacker lvl / (attacker lvl + defender lvl)
Attacker and defender can be both a player and a monster, there’s no difference.
If it rolls successfully, then the attack will proceed to check for Block.
If the attack doesn’t pass the defense check, the defender doesn’t trigger any recovery animation
BLOCK: ALL WDM attacks have to pass the Block Check, it simply uses your block chance to attempt to block the incoming attack. If the attack gets blocked, it will trigger the Block Recovery Animation.
NOTE: Some monsters also have block, and in the case of bosses, their Block Recovery will be 0 frames, so it essentially functions as a wdm specific avoid.
*insert block formula here*
AVOID: ALL attacks (wdm or not) have to pass the Avoid Check, its essentially the same as block except it doesn’t trigger an animation if it rolls successfully.


Procs Have different “bases” and “triggers”. A proc cannot scale with any kind of + skill. Procs of the same exact base but different levels roll independently of one another. If a proc is the same exact proc, down to the lvl of the proc, they become additive and only roll their chance once. (1% chance to proc lvl 1 knife, 1% chance to proc lvl 2 knife, 1% chance to proc lvl 3 knife, vs (1+1+1)% chance to cast lvl 1 knife).

WDM based procs: All arrow/javelin/knife procs scale distance with level, but their damage/wdm stays the same (50% wdm usually). These leech just as a regular attack would. They carry CB, DS and anything else a normal ranged attack would

Spell based procs: These scale with spell damage, pierce and also by their stated level.

On Attack / On Striking
On attack procs are just about any melee attack. Only a melee “slap” can proc these. Note some skills (thorn strike for example) can be cast at range, so they fall under “On striking”.

On striking procs are any %WDM trigger at all. A javelin proc can proc another javelin proc, etc.

On Kill / On Deathblow
On kill refers to killing an enemy with WDM damage or with a specific set of rules with poison damage (see poison mechanics).

On deathblow (previously “when slain”) refers to killing an enemy with any source of damage including spell damage and poison ticks. Just like wdm procs, on slain procs can chain each other.



Enemies can be brought down to -100% resistances. This amount changes depending on if the enemy is a regular mob or a boss, and what difficulty you are currently in.
Enemy res in Normal starts at 0 and doesn’t increase even for bosses.
Enemy res in Nightmare is 0 for phys/mag, 15% elemental and poison.res
Enemy res in Hell is 0 phys/mag, 35% elemental and poison, and includes a 10% chance of an addition 15% phys res (changes in sigma?)

Bosses in destruction have 35% phys/mag res, 70% elemental and poison res.

So to bring a boss to -100% res in destruction you would need 170 pierce.

Samael, Herald of the end, has 199% Elemental res, 50% physical and magical resistance, is immune to poison and is pretty much the only exception to these rules.

Immunities are changing in sigma. If an enemy “absorbs” an elemental type they are 30/50/75% resistant to that type. This cannot be reduced in any way shape or form.

► Pierce Calculations

► Spell Damage Calculations

Energy Factor:
In Median XL, direct damage spells gain a damage bonus from energy. This bonus has diminishing returns: the damage gained per additional point of energy is lower if you already have lots of energy to begin with.
The energy factor bonus on some caster items modifies this curve, causing each point into energy to provide a significant benefit until much higher levels of energy. Energy factor is particularly effective for high level characters with most or all points into energy.

The formula is as follows:
(260∗(energy+10)/250+energy) + min((energy∗energyfactor)/15000,200) = % increased spell damage

Note : Strength Factor could be thought of as Energy Factor just based on another stat. It is additive with Energy Factor and they use the same formula for added damage.


Poison can proc ‘’on kill’’ effects normally, EXCEPT if the first frame of the poison kills the target, this is only doable if you’re ridiculously overpowered for the area (ex: endgame fully geared char in normal cold plains)

Basic: poison damage is listed as the total damage over x seconds. This value however, does not take in account how fast you are actually dealing damage. To calculate that, simply divide the total damage displayed by the length of the poison (ex: our lorenado deals 1000 damage over 10 sec will be displayed as 1k in character sheet, but you’re actually dealing 100 damage per second).
%poison skill duration will increase the length of the poison while keeping the damage per second value, so if in our previous case we add 100% poison length increase, damage will ‘’increase’’ to 2000 over 20 sec (still 100 damage per second).
%poison skill damage on poison spells will increase both the total damage and the damage per second (1000 over 10 becomes 2000 over 10 under 100% poison spell damage, dps increased from 100 to 200)
-% enemy poison resistance will increase both poison length and damage per second ONLY ON MONSTERS, this is because monster’s poison resistance both lowers damage per second and poison length by the displayed amount. If with our lorenado we hit a 75% poison resist monster, we won't be dealing 250 damage over 10 seconds, we will be dealing 63 poison damage over 2,5 seconds, both cases are 25 damage per sec. This makes poison pierce especially important, because it doesn’t only improve damage per second, but also total damage.
All these stats are multiplicative with each other. (1000 over 10 with 100% spell dmg, 100% duration and -100 enemy resist becomes 16000 over 40 seconds, 400 damage per second)
Some enemies, most notably select bosses will have additional %poison length reduction, on top of their poison resist. This reduction cannot be influenced in any way and cuts length by the specified amount.

On player characters, poison length reduction is a separate stat (that is also reduced by -50% and -100% in nightmare and hell) and poison resistance only lowers damage per second but not duration.

Multiple poison sources do not stack, the highest damage per second instance will overwrite the other. This means that a 1 second poison can and will overwrite a 40 second poison if its damage per second is higher, even if total damage dealt is less. On the other hand, repeatedly attacking a target with poison will guarantee that the highest damage per second possible will be applied in case of varying dps.

► Poison Technical Stuff

► Indepth Slow information

Magic Find
Magic find only influences the “rarity” roll of an item and is one of the last rolls to happen on a drop. Therefore increased magic find only changes the number of magical/rare/set/uniques you get and has no effect on the tier of base type of the item. The item base type is first decided, then tier, then it’s rarity is rolled, if a set/unique item is rolled and there are multiple drops for that set/unique, the specific item is then decided by a roll between these available items. (Will double check this for accuracy later). Magic find does not affect shrine, rune, or quantity of item drops.

If an item rolls unique but there is no possible unique for it, it drops as a set, if an item rolls set but there is no set possible for it, it drops as a rare.

XP gain:
This stat simply increases the amount of exp you gain by a %, 100% = 2x exp gain. This is MULTIPLICATIVE with player number exp boost ( so p2 with 100% exp is 3x exp not 2.5x exp)

No Drop
No drop is basically the chance for the game to "eat" your drop. Think of it as a roll in which the game says "No, you don't get an item when you should've". It starts as a high number, and decreases in a diminishing fashion. This decreases per person that enters your game in a mechanically odd way. Conventional wisdom is that 3/5/7 decreases no drop, but it's a bit more complex than that. Technically every party member decreases no drop, as long as they are roughly within 2 screen lengths of your screen. Any member of your party which is in your game, but not within the 2 screen area decreases no drop at half the rate, which rounds down because diablo works that way which is where the 3/5/7 idea comes in. If one wanted to farm as efficiently as possible in a group setting, you would farm in 4 player games with 2 active groups of two since the no drop rate decreases diminishingly. 4 players total, 2 on one screen 2 on the other. You would get "true" 3 player no drop for each party, while only boosting monsters to 4p stats.

Small recap.
3/5/7 players in game but not actively on your screen = 2/3/4 player no drop with 3/5/7 player monster stats.

Orange Text Procs:
Amazing Grace: 5% on attack proc, turns you invulnerable (100% avoid) for 1,6 seconds.
Thunderfury: 50% on attack proc, emits charged bolts that deal 75% WDM damage with 100% lightning conversion.
Area of Effect Attack.100% on attack proc, emits a physical wdm nova (100% wdm) that hits all enemies within 5 yards from the target. Multiple novas do NOT stack, each nova hits every enemy ONCE and it can proc on striking, leech, etc.

USEFUL LINKS: ... s_eng.html - Mix of useful and technical stuff, fairly in depth ... =Diablo_II - Mix of useful and technical stuff, fairly in depth - Technical and very in depth explanation of item generation

Merc Mechanics
Many little things that I'll get around to eventually.
Odds and ends.

Seekers, Gavin, Ben-, Vampyra/Candyland, o_Owning Time, Jammy-, Kyoken, Gavin, HohoHaha, Connor, RollsRoyce and probably some I'm forgetting for help over the years.
Suchbalance, Whist, Marco, Aahz, Quirinus for the mod and their time making it what it is.
Edited by Thraxis 3 years.
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I needed knowledge and you enlighted me
Thanks and Good Work :clap:
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Hey, you are actually doing this. Thank you very much.
60 | 7
Does flat elemental damage get boosted by elemental spell damage?
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I paid 10$ for this.
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otarU1921 wrote:Does flat elemental damage get boosted by elemental spell damage?

You mean something like +100-200 to cold damage? If that's the case, no. It's added to your weapon damage, so it's not spell damage.
60 | 7
% spell damage also works with passive elemental damage sources, but only on direct melee hits.~

I am asking because of Way of the Phoenix / Spider shit like that. It gives flat elemental damage but also gives increased bonus elemental damage, so I was thinking it probably boosts itself.
Thunder Beetle
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otarU1921 wrote:Does flat elemental damage get boosted by elemental spell damage?

Yes flat elemental damage (+100 to cold damage) gets boosted only on DIRECT MELEE ATTACKS by spell damage. so 100% cold spell damage would turn that to 200 cold damage before any reductions. Certain attacks that can seem melee (thorn strike for example) do not get boosted by this as they aren't true melee attacks. Eventually I'll be going through and adding a list of things that are and aren't true melee attacks but that'll be a while.

The guide will get more added to it when I find some time. Wasn't fully completed yet, but wanted to have this up for all the new people flooding into the mod to have some info on general mechanics and a easy reference to things. Look forward to this turning into a one stop shop for all weird mechanical quirks stuff in the future.
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After all this time, I still don't know why Poison Flash does more damage when you spam it at close range compared to cast and flee.

My guesstimate is that applying poison always deals the first frame of damage and poison flash hits every frame, but this is most likely wrong.
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As a returning player, I really like this, you answered all the questions that I had or had forgotten the answer to, thank you!
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Thanks for putting this together, very informative. As you continue to add to it, can you include a section on Feedback Damage from Sorc Arcane tree? It is a very unique damage mechanic that doesn't have much info online. I've read elsewhere that Immersion and Mana Sweep act as Physical Damage, and the only way to either add Phys Damage, Phys Damage Pierce, or Feeddback Damage is with Sorc Ultimate skill, Chronofield. Trying to see if there is any other way to add Phys damage/pierce (or even Feedback Damage) to boost damage. Otherwise, increasing max mana, increasing + to skills, or increasing cast rate are the only ways to increase damage with an Arcane Sorc. I'm speccing summons from Sorc trees as well (Blade Spirits/Ice Elementals) but they act more as meat shields than damage dealers.