Guide to Understanding Broken Immunities and Monster Resistances

Since a lot of questions arise about this subject - very frequently - and I often spend lots of time typing a detailed response, I've decided to spend a few minutes "putting it all together" in one place, then hopefully I can just provide a link in the future (or, even more ideally, folks will search for answers before posting their questions, and the search tool will actually work , ... but that would be too good to be true, right?).


Where to Begin?

I think that I'll just get to the point and list a few facts about the mechanics of DiabloII and then expand from there. Understanding these facts is really all you need to know to understand this aspect of DiabloII.

1. Monsters are considered "immune" when their resistance to an element is 100% or greater.

2. Conviction (the Paladin aura) and Lower Resistance (the Necromancer curse) and are the ONLY two methods of removing a monster's elemental immunity*.

Note#1: There are several different types of "elemental immunity", but at the moment I'm referring exclusively to the Lightning, Fire, and Cold elements. Physical, Magic, and Poison are the other "elements", but those will be ignored - for the moment, and unless otherwise specified.

Note#2: The Lower Resistance curse will often be referred to as "LR" within this guide (and other posts).


3. When working against an elemental immunity, Conviction and LR always work at 20% effectiveness. Always. If you use both together, but only one of them would be necessary to remove an immunity, they both will still receive this penalty.

4a. Other methods to lower an enemy's resistance (Cold Mastery, Rainbow Facets, -Enemy Lightning Resistance on Griffon's Eye, etc.) cannot remove an immunity. However, if these methods are working against a non-immunity (or a "broken" immunity), they will always work at 100% effectiveness.
4b. These methods will ONLY work for the person "wielding" them (so the -Enemy Lightning Resistance on your mercenary's polearm will not improve your sorceress' lightning damage - it will only improve your mercenary's lightning damage).

5. The lowest that a monster's resistance to any element can be lowered is to a final result of -100%. (For the PvP crowd, this also is true against enemy players and minions).



Example Scenarios
As I said previously, once you understand those 5 facts, that's really all there is to know. However, just to (hopefully) make sure it's clear, here's a few examples to illustrate it.

To help keep it simple, all examples will assume that you're playing a lightning sorceress that wears a perfect, faceted Griffon's Eye (-25% Enemy Lightning Resistance), and that sorceress's mercenary is wielding an Infinity polearm (level 12 Conviction aura).


Example #1: Your sorceress encounters a monster with 0% lightning resistance.

- The merc's Conviction aura is not facing an immunity, so it will work at 100% effectiveness. This alone will lower the monster to -85% lightning resistance. However, the Griffon's Eye will lower him further by 25% (bringing the monster to -110%) ... except the lowest a monsters resistance can go is -100% total, so the game will "limit" this number in it's calculations. Don't worry about the lost 10% however, because this will quickly become a dead monster.


Example #2: Your sorceress encounters a monster with 105% lightning resistance. (remember, it is possible for an "immunity" to be greater than 100%).

- The merc's Conviction aura is facing an immunity, so it will only work at 20% effectiveness (-85% divided by 5 = 17% lower resistance against an immunity). This will lower the monster to a total of 88% lightning resistance. However, the Griffon's Eye will lower him further by 25% - and it works at 100% effectiveness. When your sorc casts a lightning spell, the monster will have 63% lightning resistance. The merc's Infinity also comes with "Lowers Enemy Lightning Resists", but that only benefits your merc (so if his attack has lightning damage, his damage will benefit from this mod - but he won't benefit from the Griffon's Eye the sorc is wearing).


Example #3: Your sorceress encounters a monster with 105% lightning resistance, and in addition to the merc's Infinity, you're questing with a necromancer that casts level 15 Lower Resistance (-60%).

- The merc's Conviction aura is facing an immunity, so it will only work at 20% effectiveness (-85% divided by 5 = 17% lower resistance against an immunity). Even though the Lower Resistanct curse will not be required to "break" the immunity, it will still suffer the 20% effectiveness penalty (reducing it from -60% down to -12% benefit). So that leaves the monster with 76% resistance, then the sorc's Griffon's Eye will lower it to 51%.


Example #4: Your sorceress encounters a monster with 180% lightning resistance.

- Conviction tops out at -150% resistances at level25 (or -30% resistances against an "immune" element, because of the 20% effectiveness penalty). Increasing it's skill level will not improve this. Lower Resistances gets boosted by a small amount for each level gained, but even at level 50 it only provides 69% lower resistances (which is only 13% after the 20% effectiveness penalty). Adding that all together, the monster is left with 137% lightning resistance, and there's no other way to lower an "immunity".

... this is what is referred to as an "unbreakable" immunity, and if you want to damage this monster with your lightning sorc, you're going to have to whack him with a normal attack (or cast a "backup" skill from the fire/cold tree). As an interesting sidenote, the 'knockback' on Telekinesis will work against Lightning Immunes, but the monster won't receive any damage. For a lightning sorc without a backup attack, keep this in mind since it can help your mercenary by helping stun-lock the monster (so the merc can attack and the monster can't retaliate).



Wait... you just mentioned 180% Lightning Resistance on a monster... How will a monster get such a high resistance?

There are three methods that can increase a monster's resistance to a specific element - and all of these methods only apply to "boss" monsters (in this case, a "boss" refers to any monster that spawns with random monster bonuses and has a 'unique' name - for example the Ancient's you face on Arreat Plateau qualify, as do any random monster you meet that's named "Snot Reaper").

If a "boss" monster spawns as Fire / Cold / Lightning Enchanted, then it will gain 75% resistance to the specified element (so, a random Death Beetle "boss" you encounter in Act2 Hell that happens to spawn with Lightning Enchanted will end up with 180% Lightning Resistance: 105% inherent resistance, +75% from Lightning Enchanted).

The second way to increase a boss' resistance is when he spawns as "Magic Resistant". In this case, it will add 40% to the cold, fire, and lightning elements (individually, and in that order). This mod can (and will) stack on top of the "<element> Enchanted", providing a total combined boost of 115% to a specific element.

The final way to increase a boss' resistance is when he spawns as "Spectral Hit". This works in the same manner as Magic Resistant, but will only add 20% to each of the cold, fire, and lightning elements (again: individually, and in that order).


As a sidenote, in the current version of DiabloII, 99.9% of the monsters in the game can only have a maximum of TWO immunities. If multiple mods spawn and the monster should have a third immunity, the third bonus is simply not applied. The exception to the "maximum two immune elements" rule are Pit Lords that you encounter during ?ber runs, which have immunities to everything except Physical Damage and Blessed Hammers (why Blessed Hammers work is explained below).

Also, the order for determining which elements become "immune" first is pretty simple: It's the order that the modifications are listed. So if a (theoretical) monster starts with 50% to each resistance and spawns "Fire Enchanted, Cold Enchanted", he will become fire immune first, andafter that it will attempt to become cold immune. However, if that monster had a natural poison immunity when those monster bonuses spawned, the attempted cold immunity would not supplant the poison immunity - the monster would remain poison immune and gain a fire immunity, but it would not add the third immunity (cold).

It's the intricacies that make this somewhat complicated to explain clearly (hopefully the last paragraph wasn't too overboard), but hopefully another list of examples will illustrate it. Feel free to skip the rest of this section if... you're not concerned with the exact details of when a monster will spawn fire vs. cold immune because of its random mods - it's probably more detail than you need or want. But, if you're reading this and/or really want to know... don't say I didn't warn you.

We'll expand on the theoretical random boss monster that has 50% for every resistance:

- If it had spawned "Fire Enchanted", "Cold Enchanted" and "Lightning Enchanted"... the boss would become Fire and Cold Immune, and would remain with 50% Lightning Resistance (remember: the boost to create the impossible third "immunity" is simply dropped).

- If it had spawned "Lightning Enchanted", "Fire Enchanted", and "Cold Enchanted"... the boss would become Lightning and Fire Immune, and would remain with 50% Cold Resistance.

- If the monster had started with a natural Poison Immunity and then spawned with "Fire Enchanted", "Cold Enchanted" and "Lightning Enchanted"... the natural poison immunity would remain and the monster would only gain one immunity (to the first element listed in its mods - in this case "fire"). This is because of the "maximum of two immune elements" rule. The other two elements (cold & lite) would remain at 50%.

- Because the "Magic Resistant" and "Spectral Hit" mods apply their bonuses in a certain order (cold, then fire, then lightning), if these both were to spawn on the theoretical boss with 50% resistance to every element:

a) if "Magic Resistant" is listed first, the monster would end with cold and fire immunities (110% resistances) and a lightning resistance of 90%. (In this case the +40% from "Magic Resistant" would be applied, but the +20% would attempt to create a third immunity, which is why it isn't added).

b) converse to that, if "Spectral Hit" is listed first in that monster's bonuses, the monster would end with 110% fire & cold resistances, and only 70% lightning resistance (because Spectral Hit's +20% is applied first, and the +40% from "Magic Resistant" would try to create third immunity and therefore get dropped).

... meh, hopefully that's clear enough. If not, it's already too long-winded, so either re-read it carefully or don't worry about it. I'd truly recommend the latter. So, moving on...


Monster's Natural Resistances
Since the information fits here as well as anywhere else in this guide, monsters that are inherently immune to an element generally (but not always) have a resistance value that falls in this amount:

Lightning Resistance: 100 - 110%
Fire Resistance: 110 - 130%
Cold Resistance: 150+%
... and ...
Poison Resistance: 100-110%
Physical Resistance: 100-110%
Magic Resistance: 100+% (this one doesn't matter as much as the others - you can only influence magic resistances with a Paladin's Sanctuary aura, which is always bugged to lower 'undead' monsters to 0% resistance, and doesn't work against non-undead)

... so, if you look at those numbers, you'll realize that a monster that is naturally lightning immune is much more likely to have it's "immunity" removed by an Infinity polearm wielded by a mercenary. Likewise, Cold "immune" monsters often have such a high resistance that no amount of Conviction and/or Lower Resistance can remove that immunity. Fire immunities can sometimes be broken by the Infinity, but I wouldn't count on it to be reliable.

There are specific exceptions to these examples, and you can find detailed info about various monster's naturally inherent resistances to elements here. (Sidenote: I'm not guaranteeing the accuracy of that data - Arreat Summit has a somewhat-deserved reputation for inaccurate data).


The Other Elemental Immunities:
Magic: As mentioned previously, you can only "break" this immunity with a Sanctuary aura against an undead monster.

Physical: Two necromancer curses can "break" a phyical immunity. Amplify Damage, and Decrepify. Since they're both curses, they overwrite each other... so only one can be active at one time on a single monster. These curses both receive the 20% effectiveness penalty against a physical immunity, the same way that Conviction and LR suffer the penalty against elemental immunities. Also FYI, a boss monster that spawns "Stone Skin" will gain a 50% Physical Resistance (assuming AS is correct - and I'm not sure it is). Conviction and LR will notaffect this immunity or resistance.

Poison: The Lower Resistance curse is the only method that can "break" a poison immunity or lower this resistance (Conviction only works against fire, cold, and lightning resistances). As a bonus, there are no mods that will boost a monster's poison resistance, so a decent level LR curse will hopefully do the trick.


Blessed Hammers:
This doesn't really fit anywhere in this guide, but it's somewhat related, so I'll include it.

Blessed Hammer, the paladin skill, deals 'magic' damage. And it will work at full damage against 'undead' and 'demon' type monsters, even when the undead/demon spawns as Magic Immune. There is a third monster type ('animal') that Blessed Hammer does not work against when the monster spawns Magic Immune.

Edit: This appears to be changed in version 1.13 - Blessed Hammers will no longer bypass Magic Immunity for undead/demon type monsters. That's the way it is for the beta release at least, and I suspect the final release of version 1.13 will keep this change.


THANKS
A lot of folks have provided clarifications & corrections to this work-in-progress.

I originally tried to mention them by name throughout the guide, but there were enough corrections that I felt it was obstructing the flow of the guide. So I moved the "thanks" down here. Also, it's possible/probable that I missed one or two (or ten - I'm not that good with fine details ) in my list, which would be unfair to those I missed, so I'm no longer mentioning folks by name. Even though they deserve that much credit (and more) for their help.

So, thank you to the many that have helped improve this resource.