[2.0] Mjolner life based Rainbownuke witch, !!Deathless 82 Core/Uber!!

16.07.15 - Added Screenshots
16.07.15 - Added Atziri video
16.07.15 - Added Doedre's Tenure as gloves under the gear section
16.07.15 - Added reflect map video
16.07.15 - Added link to skieZ's build as an end-game option
16.07.15 - Spellchecking and changing wording on some parts of the guide
16.05.15 - Added Leveling section
17.07.15 - Uber Killed. Changed title
17.07.15 - Added Uber video
17.07.15 - Slight change to passive skill tree
17.07.15 - Updated screenshots
17.07.15 - Added notes on life leech in the event of no Kingsguard
19.07.15 - Added my new pair of gloves in the gear section, with some explanation
19.07.15 - Added jewel section
21.07.15 - Removed text about accuracy. Quality accuracy is fine now
02.08.15 - Added large sections about the new passive skill tree.
02.08.15 - Updated gem section for the new passive skill tree
02.08.15 - Updated "my gear" section
05.08.15 - Uploaded many new screenshots
05.08.15 - Added Scolds Bridle in the gear section
09.08.15 - Updated banner (thanks, Krux)
09.08.15 - Edited large number of typos (Thanks, Krux)
09.08.15 - Changed some text to make the guide easier to understand (Thanks, Krux)
09.08.15 - Added more comprehensive analysis of Lightning pen vs Iron Will
11.08.15 - Added more banners and made some sections easier to understand (Thanks, Krux)
14.08.15 - Added detailed math behind Iron Will vs Lightning Pen
09.09.15 - Total revamp of the guide (Thanks, Krux)
09.09.15 - Deathless Uber and 82 Core videos added (Thanks, Krux)
09.09.15 - New, more readable banners (Thanks, Krux)
09.09.15 - Build version 3 "Armor Life MoM/EB" added (Thanks, Krux)
14.09.15 - Uber Video guide added for "Armor Life MoM/EB" build (Thanks, Krux)
19.09.15 - Fixed gems for "Armor Life MoM/EB" (Thanks Krux)
19.09.15 - Added a brief description of all 3 versions of the build for ease of use.
19.09.15 - Moved the "Lightning Penetration vs Iron Will Math" to Post #2

This build used to be a Low life version of the popular Rainbownuke Mjolner build, made by Tom94. As of 2.0, Low Life has taken a huge hit and was also indirectly nerfed by other changes in 2.0.
Luckily, GGG was kind enough in granting us tools to make up for the nerfs by utilizing Life instead of Energy Shield. Here are some, but not all, reasons why I chose to make this build Life-based in 2.0:

- Blood rage: No longer grants 40% IAS on Low Life, instead granting up to 20% IAS for everyone. Degen is now based on both Life and Energy Shield, and deals Physical damage instead of Chaos damage.

- Introduction of Jewels: Jewels have the potential to be incredibly powerful, granting up to 8% life and a variety of other powerful MODs, such as Attack speed, Damage, Crit, ES on Hit etc. Life-based Mjolner builds now have an easier time getting many of these Jewel slots.

-Immortal Call nerf: This affects both Life-based and Low Life Mjolner builds, but it all comes back to survivability. We cannot solely rely on Immortal Call for Physical mitigation anymore. Life-based builds seem to have more options in this regard.

- Reduced Mana nerf: Pretty self-explanatory. With the nerf to the Reduced Mana gem, we cannot use as many auras as we used to, hence we get less damage from our investment in auras.

- Leech nerf: This was the biggest cause of concern for me when it comes to Low Life Mjolner builds. It means that, with a Low Life build, one cannot just nuke away on any boss and expect that their Life leech will keep up. On the other side of the coin, a Life-based Mjolner build provides more defenses to both mitigate and regain life in boss fights, mostly because of the following item:
This item is so strong for the Life-based builds. We Discharge so many Endurance charges each second, that 100 Life for each of them is a huge regen buff. We are looking at 3-4k life per second, as long as we're hitting something.

- Uber Atziri viable, deathless.
- Core 82 viable, deathless.
- High clear speed.
- Insane leech and survivability.
- Immune to reflect.
- Near impervious to any Elemental damage.
- 3 versions of the build: 1) "Life DPS", 2) "Armor Life", and 3) "Armor Life MoM/EB").
- Very sturdy against high physical damage ("Armor Life" and "Armor Life MoM/EB" versions).
- Additional options make end-game Chaos Damage bosses easy (Village Ruin amongst others).
- The build is 100% compatible with Witch and Marauder (Build version 3)
- Pretty, pretty colors :D

- "Life DPS" version of the build can be vulnerable to high physical damage.
- Can be expensive for post 2.0 newcomers to the Mjolner world who need all of the gear.
- Proper Jewels for version 3) "Armor Life MoM/EB" can be hard to craft/expensive to buy.
- RIP frames. Not a build for low-tier PCs.

Uber Atziri (Viviere)
Using "Life DPS" version of the build.
First attempt and kill. Not a flawless run, deathless all the way up to Atziri though. "Life DPS" version seems to be suffering from her Spears, causing me to die more than once. Accuracy was lacking too at this point, I felt, as on this high-level map I didn't get the flask charges that I should've gotten from hitting mobs.
Update: After switching to the "Armor Life" version of the build, I've killed Uber Atziri many more times. No deathless runs, had a couple attempts where I was clipped by Flameblast at the very end. However, the "Armor Life" version enables me to facetank everything in the Alluring Abyss, with the exception of her Double Flameblast. The Trio boss becomes almost a joke with the "Armor Life" version, as I can mostly facetank them without a big hassle. So without being clipped by the Double Flameblast, deathless runs are 100% doable.

Uber Video Guide for the "Armor Life MoM/EB" version of the build (Krux)
Using "Armor Life MoM/EB" version of the build.
The guide covers only how I setup for my deathless Uber runs. Namely: CWDT, gem and flask setups. Features full boss fights
This is my first video guide ever, so be gentle :)

Uber Atziri (Krux) deathless
Using "Armor Life MoM/EB" version of the build.
The video is sped up like x4. It's purpose isn't to educate on the fight, but rather to give a small showcase of the "Armor Life MoM/EB" version of the build and to test a few things. My upload limit is only 1Mbit which played a big part in speeding up the video, so I don't have to wait 6+ hours for the upload to finish. Bottom line, deathless runs are very much a "been there, done that" thing with this version of the build.
Few notes:
1) I didn't use RF on Vaals as this was my 'practice run'. I wanted to fight the enraged Vaal for a bit. Needless to say, the fight lasted way longer due to this.
2) On Trio, again in the spirit of 'science', I fought the Titty bitch last. It got quite hairy, with a few very close calls. Again, Trio fight lasted longer than usual. Not something I'll willingly do again, unless we're testing stuff.
3) No testing on Atziri this time around. Just flat out kill.
Please note that after 2.0, deathless runs shouldn't be taken for granted or expected 100% of the time. This was my 2nd deathless run in a row, but dying is till very much a part of the 2.0 Alluring Abyss. That said, we've clearly shown that the "Armor Life MoM/EB" version can very much do deathless Uber runs.

82 Core (Krux) deathless 4 boss fights, 4 videos.
Using "Armor Life MoM/EB" version of the build.
Prodigy of Hexes
Prodigy of Pain
Prodigy of Darkness
Eater of Souls
This is where the "Armor Life MoM/EB" version truly shines. Its' mitigating capacities are fully utilized in this brutal map. Learning the boss mechanics is a plus of course (you can practice spotting animations in the Merciless A4 boss fight), but even in the lvl82 runs that I died in, I still felt the true power of this build version and it was just amazing how much punishment I can take.
Note: Upload took forever so I had to upload the boss fights separately. #1Mbitupload :(

81 Palace double boss turbo (Viviere)
Using "Life DPS" version of the build.
Some explaining is needed here. During the boss fight, I had a client crash (I suspect it was related to my recording codec). The footage was fine all the way up to the crash, while the footage after the crash got corrupted, making it uneditable. Would've like to show it here, so someone could explain what might've happened.
The fight itself was fairly intense. Twin boss/Boss turbo/Monster life (47%) and half regen. I would take a lot of damage if my flasks weren't up at all times in Phase 1. The fight is slow, as I used Lightning Strike which wasted 2/3 of my Discharges, because I never dared to get up into their face and nuke them. I was afraid of getting one-shotted by Touch of God (had 99% resist, 12k Armor, Fortify, 4 x Endurance charges and Chaos golem in the video).

79 Village ruin (Krux)
Using "Armor Life MoM/EB" version of the build.
MODs: Boss damage (35%), Boss attack/cast speed (30%) / Vulnerability. I thought this would hurt. But again, this build version shined. I used a Amethyst flask (Surgeon/Reflexes) and a Chaos Resistance ring. With a total of 30% Chaos Res I almost wondered why was I ever afraid of this boss. Even when paralyzed I just toughed it out and stood in the poison clouds. Facetanked the Archer 95% of the fight, ran out only once near the end.

76 Residence (Reflect) (Viviere)

On your remaining items focus on Life/Res/required Attributes/Damage. More specifically, besides finding gear with life (or Master-crafting it yourself), you should fill out your Resistances, get enough Attributes (STR, INT or DEX, whichever you lack) and get whatever damage boosts you feel you can afford. Getting enough attributes from gear can be a challenge, but it is advisable so that you don't have to waste passives. For damage sources on gear look for Spell Crit, Spell Damage, Attack Speed and Accuracy. Keep in mind that we do not want Melee Crit as it eats our Power Charges due to Romira's Banquet. This results in a weaker Discharge.

Here are some examples:

Off-hand

Saffell's frame is great for your resistances and will make you near reflect immune. This is the legacy version, but if you're using a non-legacy Saffell, you can still get good mileage out of it and perhaps upgrade to legacy for the very end-game.

Helm

This is the prefered helmet in this guide. Devoto's Devotion provides so much to us: 1) Attack speed, 2) Movement speed, 3) 1k Armor, 4) Dexterity. The physical damage reduction means nothing.

Belt

Again, the focus is on Strenght, Life and Resists. Armor and Flask recharge are a plus.

2nd Ring

Get STR/DEX/INT, whichever you lack, Resistances and Life. Anything else is a bonus. Attack speed, Accuracy etc.

Boots

Same rule applies here. Get whatever STR/DEX/INT you need, get Resistances, get Life. Anything else is a bonus, primarily Movement speed.

Gloves

These are the prefered gloves in this guide. However, they are sometimes hard to find on the market and due to this can be very expensive. Prices literally range from 25 - 80exa for this item. If you cannot obtain them, for whatever reason, check out the "Gloves" section in the "Other gear options" below.
The +1 Implicit MOD on Voidbringer allows us to save a lot of passive points and it frees up 3 Skill gem slots in our gear, which in turn allows us the space for a movement skill (Leap slam, Lightning warp). By placing 21/20 Purity of Fire and Purity of Lightning, they will both reach level 23 without the use of the Empower gem. All 3 versions of the build will benefit heavily from this item. Depending on the version build used, there are trade-offs but they are very much worth it.

Focus of the build is to get as much Spell damage, Life, and Spell Crit as possible from the passive tree, while still getting the needed Strength, Intelligence and Dexterity from gear to support our Mjolner and gems.
Bandits: Oak, passive, Oak
Jewel slots available: 5
Passive tree
Gear:


Flasks:


Jewels:


Gems:
Auras:
This version runs 3 or 4 auras, depending on what might be needed at any given time. Two auras that are always present are:

These two Purities grant defense against what are, arguably, two most dangerous Elements in the game. It's ok to run Purity of Ice as well, although Cold damage just doesn't seem to be that scary so there's really no pressing need for this aura.


Link these two with PoL and PoF. The aim is to reach level 23 on your Auras by having level 21 Auras + level 3 Empower. Enlighten level 3 is required to reduce mana reserved cost.

Other auras, depending on the situation:

or

Haste grants the biggest DPS boost and increases movement speed as well. Movement speed is key in this version of the build as we do not have a movement skill in our setup.
Herald of Thunder + Arctic Armour is a better defensive option and comes pretty close to Haste when it comes to damage, but at the cost of the movement speed buff.



Mjolner gems:

Pretty straightforward, this is a Discharge build :D


Our secondary damage skill. A must have, as it grants us charges when it does not crit, yet it does not consume charges when it crits. This means that Arc will always grant at least 1 Power Charge and one Endurance Charge when it hits a target. If it crits, nothing happens, because the crit will be factored in after Discharge is triggered, so there is no need to worry that Arc will ever consume your Power Charges through Romira's Banquet.


With this version of the build, Lightning Penetration beats Iron Will in every scenario. I could show you the math, but I'm lazy. Just trust me on this.

Attack skill:
Now, here is an interesting one. You have a fair bit of choices on this one. For a 5-link, your main attack skills will be

Supported by

Molten strike is by far the best for single targets, while Lightning strike shines when there are big packs of mobs to be cleared. None of these two need levels, as their levels grant nothing for us exept increased mana cost. *note* DO NOT GET QUALITY LIGHTNING STRIKE. This will actually lower your DPS. Mjolner has a built in + 1 chain, wich we utilize to great effect with Lightning strike. If you pierce, you can't chain. No chain = less procs. GMP, Faster attacks and Multistrike are all used to get as many hits down as possible, in order to proc the Mjolner as fast as possible. Blood magic is used to sustain it, since we reserve all of our mana.

Now, if you manage to get a 6th link, there are some fun things you can do. First off, let me just emphasize, that the new content HURTS. Keep this in mind when you choose your sixth link. As I see it, you have 4 choices: Go the utility way, by placing BOTH your molten strike and your lightning strike in there, and be able to use them both situationally. The second option is damage. There are two choices here;

LMP will statistically grant more hits per second, and therefore higher dps. Accuracy will grant more consistent hits, giving you less room for a "downtime".

The third option is to go defencive. this can be achieved by using

Fortify Grants us 20% reduced damage taken from hits, for 5 seconds. This means all hits, elemental, chaos, or physical. This is an extremely strong defensive option, and my personal favourite.

CWDT setup:
We do have a Cast when damage taken setup, for defensive purposes


You might think that these have oddly specific levels, but there is a reasoning behind it. I do not want a max level CWDT, because that would mean I have to take 4k damage before it procs. Level 14 CWDT comes with a fair amount of benefits though. Let me explain:
Immortal call now gets less effectiveness from Increased duration, and more from Endurance charges and levels. It now also has an internal cooldown of 3 seconds. The reason I chose to keep it at level 16 is that this is the threshold after which Immortal Call will last longer than 3 seconds, given that you have 4 endurance charges and a 20/20 increased duration. To be exact, it will last 3.016 seconds. In most cases, I will have 4 endurance charges after i discharge. Meaning that i at least have the theoretical potential to keep 100% uptime on Immortal call. And by keeping it at level 16, it can be triggered by a lvl 14 CWDT, wich only requires 1900 life to trigger, which is within reason. Enfeeble is just there to reduce enemy damage even further, minimizing the risk of death.

Rest of the gems:
The rest of my gems are used for a couple of things that I find handy, most notably

Chaos Golem is used simply for extra mitigation, Blood Rage is used for extra DPS. Blood rage grants 20% attack speed and a chance to gain frenzy charges on kill, further amplifying discharge damage. I do not have the health regen to completely negate Blood Rage though, so use it with caution.
Note: Armor-based tree has enough life regen to support Blood Rage
Chaos golem gem can be swapped out with the Flame golem or Ice golem if you prefer, but personally I like the defenses it provides. Both of these gems will of course be linked with

Another nice option to add to these gems if you want to is
This increases both the golems power and the Blood Rage power.

If you prefer, it is entirely possible to drop Blood rage and go for a movement skill instead. Personally i do not feel that I need it, as I have 60% increased movement speed with haste up, and a permanent quicksilver flask of adrenaline. Im going fast enough.

If you want, you can also use

For bosses. This will greatly boost your spells, to the point of double damage for Discharge

Focus of the build is to gain massive amounts of Armor, at the cost of a tiny bit of damage. The idea is to move down to the Marauder/Duelist area and grab as many armor nodes as possible, grab Iron Reflexes, and use the Grace aura. This version of the build uses only 6% Reduced Mana Reserved on the Passive tree as Empower is no longer needed to reach level 23 Purities. However, this assumes that we're using Voidbringer with the +1 to gems corrupted implicit MOD.
If you still need Empower to get level 23 Auras, then you need to spend a few more points in Aura reduction.
You can still use non-corrupted Voidbringer and go without Empower but you will lose some Resistances.
On the passive tree, it is much easier to reach the Strength needed for Mjolner but it's a bit harder on the Intelligence side. In short, less STR needed on gear, some more INT needed.
This build can take you to the very end-game.

Bandits: Oak, passive, Oak
Jewel slots available: 5
Passive tree
Gear:


Flasks:


Jewels:


Gems:
Auras:

As it was already mentioned, Void +1 allows us to reach level 23 Purities without Empower. This frees up passive skill points, allows Grace to slot it instead of Empower, and AA + Herald of Thunder are dropped. 35k Armor is easily reachable with this tree, and 40k+ at higher levels. This Aura setup greatly reduces the threat from high physical damage. Also, a few gem slots are freed up that we can use for a movement skill (Leap slam, Lightning coil).

Mjolner gems:

Pretty straightforward, this is a Discharge build :D


Our secondary damage skill. A must have, as it grants us charges when it does not crit, yet it does not consume charges when it crits. This means that Arc will always grant at least 1 Power Charge and one Endurance Charge when it hits a target. If it crits, nothing happens, because the crit will be factored in after Discharge is triggered, so there is no need to worry that Arc will ever consume your Power Charges through Romira's Banquet.


After extensive math and practical testing on this, the conclusion is: No, Conc Effect or Iron Will are not better.
With this version of the build, a 20/20 Iron will beats Lightning Penetration as long as the target has less than 20-ish % Resistance, because we get a lot less pure Spell Damage or Elemental damage from the Passive tree, making the boost from Iron Will much greater. This, however, might not be the case for everyone. Depending on your own specifics and deatils, Iron Will may or may not beat Lightning Penetration.


Empower increases your Discharge output by roughly 15%. It's not quite as powerful as Iron Will or Lightning Penetration in most scenarios, but worth mentioning.

Attack skill:
Now, here is an interesting one. You have a fair bit of choices on this one. For a 5-link, your main attack skills will be

Supported by

Molten strike is by far the best for single targets, while Lightning strike shines when there are big packs of mobs to be cleared. None of these two need levels, as their levels grant nothing for us exept increased mana cost. *note* DO NOT GET QUALITY LIGHTNING STRIKE. This will actually lower your DPS. Mjolner has a built in + 1 chain, wich we utilize to great effect with Lightning strike. If you pierce, you can't chain. No chain = less procs. GMP, Faster attacks and Multistrike are all used to get as many hits down as possible, in order to proc the Mjolner as fast as possible. Blood magic is used to sustain it, since we reserve all of our mana.

Now, if you manage to get a 6th link, there are some fun things you can do. First off, let me just emphasize, that the new content HURTS. Keep this in mind when you choose your sixth link. As I see it, you have 4 choices: Go the utility way, by placing BOTH your molten strike and your lightning strike in there, and be able to use them both situationally. The second option is damage. There are two choices here;

LMP will statistically grant more hits per second, and therefore higher dps. Accuracy will grant more consistent hits, giving you less room for a "downtime".

The third option is to go defencive. this can be achieved by using

Fortify Grants us 20% reduced damage taken from hits, for 5 seconds. This means all hits, elemental, chaos, or physical. This is an extremely strong defensive option, and my personal favourite.

CWDT setup:
We do have a Cast when damage taken setup, for defensive purposes


You might think that these have oddly specific levels, but there is a reasoning behind it. I do not want a max level CWDT, because that would mean I have to take 4k damage before it procs. Level 14 CWDT comes with a fair amount of benefits though. Let me explain:
Immortal call now gets less effectiveness from Increased duration, and more from Endurance charges and levels. It now also has an internal cooldown of 3 seconds. The reason I chose to keep it at level 16 is that this is the threshold after which Immortal Call will last longer than 3 seconds, given that you have 4 endurance charges and a 20/20 increased duration. To be exact, it will last 3.016 seconds. In most cases, I will have 4 endurance charges after i discharge. Meaning that i at least have the theoretical potential to keep 100% uptime on Immortal call. And by keeping it at level 16, it can be triggered by a lvl 14 CWDT, wich only requires 1900 life to trigger, which is within reason. Enfeeble is just there to reduce enemy damage even further, minimizing the risk of death.

Rest of the gems:
The rest of my gems are used for a couple of things that I find handy, most notably

Chaos Golem is used simply for extra mitigation, Blood Rage is used for extra DPS. Blood rage grants 20% attack speed and a chance to gain frenzy charges on kill, further amplifying discharge damage. I do not have the health regen to completely negate Blood Rage though, so use it with caution.
Note: Armor-based tree has enough life regen to support Blood Rage
Chaos golem gem can be swapped out with the Flame golem or Ice golem if you prefer, but personally I like the defenses it provides. Both of these gems will of course be linked with

Another nice option to add to these gems if you want to is
This increases both the golems power and the Blood Rage power.

Using this version of the build, it is easy to chuck in a movement skill into your off-hand

If you want, you can also use

For bosses. This will greatly boost your spells, to the point of double damage for Discharge

Some of the very end game content is brutal, so the aim of this version is: Even more survivability. We achieve this by utilizing our Energy Shield + Cobalt Jewels with the MOD "ES on Hit" (short for: "Energy Shield gained for each Enemy hit by your Attacks"). In short, the effect of Kingsguard + ES on Hit Jewels is two-fold: 1) We have much more flat life, 2) Our main attack skill regenerates both our Life pool and Energy Shield pool simultaneously (Blood Rage gem is dropped to make this work). Last, but definitely not least, Mind over Matter gives us additional 30% mitigation. The multi layered defenses of this version improve our quality of life immensly vs the very end game.
NOTE: (Sep 9th, 2015) Some testing is underway to perhaps drop the BM gem. Small changes to the build are still possible, nothing that should discourage you from crossing over to this version of the build. Stay tuned.

Bandits: Oak, passive, Oak
Jewel slots available: 5
Passive tree
Gear:
Enfeeble in the boots should be 20/20. Additionally we have two other gems for Boots. Minion Life and Elemental Weakness, both 20/20, instead of Enfeeble depending on the situation.

Flasks:


Jewels:

The big change here is the Jewel MOD priority, and they are split in two. Primary MODs: ES on Hit/Life. Secondary MODs: Damage/Crit/Attack speed in no particular order (consider yourself lucky if you get any + ESoH/Life MODs). The split between Primary and Secondary is made due to the fact that ES on Hit + Life are hard to roll, let alone rolling them with useful Damage MODs. Crafting these Jewels and/or buying them can be a bit tedius and expensive (if the aim is to achieve perfect quad-MOD rolled Jewels).
Tip on Jewel rolling: Alt/Aug them until you get ESoH + Life, then Regal for Damage MODs, then yolo Exa if you get 3 useful MODs. Jewels linked here for this build version are, as you can see, far from perfect. Don't get discouraged if you fail in getting the right MOD combos. It'll all pay off in the end :D

Gems:
Auras:

PoL - PoF - Enlighten lvl3 - Grace

Mjolner gems:

Discharge: Pretty straightforward, this is a Discharge build :D
Ball Lightning: Higher proc rate, more flask charges.
Lightning Penetration
Regarding the "LP vs IW" discussion: It's expected that, for this build, we are using Devoto's Devotion, therefore Lightning Penetration and Iron Will are practically even. The differences are:
1) Iron Will beats out Lightning Penetration on low resistance targets.
2) Lightning Penetration beats out Iron Will on high resistance targets.


Empower increases your Discharge output by roughly 15%. It's not quite as powerful as Iron Will or Lightning Penetration in most scenarios, but worth mentioning.

Attack skill:
It's assumed you have a 6L for this build:


CWDT setup:


CWDT 2 setup:

Chaos Golem lvl20, CWDT lvl20, Minion Life lvl20, Enhance lvl4 (lvl 3 works too).
Aim of this version of the build is to enable us to take some heavy punishment, having a auto-cast Chaos Golem setup is needed. Self-casting a Golem in those long brutal boss fights? Ain't nobody got time for that!"
Bottom line: The 4% reduction in damage taken can be a life saver. So give your Golem a bit of love with those 20/20 Gems and perhaps Enhance lvl4 as it'll increase the minion's life pool a lot, making it even more useful.

Chaos Resistance Options:
Some Chaos resistance items can help us in boss fights like the Village Ruin, Prodigy of Pain, and even Uber Trio boss, depending in which order you kill them.

Additional damage gem:

For bosses. This will greatly boost your spells, to the point of double damage for Discharge

I will try to keep this guide up to date, as new things and balance changes to items and gems are surely to follow. BUT, in the event of any major rehaul on anything that is mandatory for this build, I seriously can't even........ I won't bother to redo the entire guide in the event of a cataclysmic patch. Fair warning

This example will be for my personal gear and gem setup (Viviere). ive found some theese numbers through testing With the use of doedres flask and some by doing math

For me, Iron will grants me roughly 30% more damage. this is universal, and does not care how many charges i currently have on discharge, or how much crit i have, or anything else. 30% more damage to both arc and discharge, bam. Edit: This number is easy to find for yourself. just use doedre flask to put you on max charges. Then, see how much damage you deal with and without Iron will in your gem setup. take the lower number and divide it by the bigger number. in my case, this gave me a number of 0.70. Take 1 and subtract the number you got (0.7 in my case). 1 - 0.7 = 0.3. 30%

Lightning pen however, is a different story. first, you need to find out, how many % of your damage is actual lightning damage. Through testing and calculations, ive found out that with 3/4/0 charges (wich will be most boss fights) Roughly 75% of my damage comes from lightning damage. With 3/4/1 (wich will be the average trash pack discharge) the number shrinks to 70%. So lets use the 70% number for the rest of this calculation.

In this calculation, the actual damage of your own discharge does not matter one single bit. the only thing that matters is how many % of your damage is lightning, and how many % will your damage increase if you use iron will.

So, lets take a random number. 10 000. This is your damage on one proc (both arc and discharge combined). Your target in this case has 0% resists. With an iron will support gem, this damage will go up by 30%. Meaning you now deal 13 000 damage.

With Lightning pen, the math gets a bit more complex. so we know that 70% of our damage is lightning damage. in this case, thats 7000 damage. The 3000 other damage will be fire + cold damage. This is then multiplied by 37%, this is the penetration of your lightning pen. that gives us a number of 9590. This is how much lightning damage you deal to a 0 resist target. now add the fire+cold damage (3000) back onto this lightning number. 9590 + 3000 = 12590 damage.

Now lets add resists to this math. Again, we deal 10 000 damage, 13000 with iron will. But now, our target has 20% all-res. We multiply our damage with 0.8 because of this. 13 000 x 0.8 = 10400. This is our damage with iron will, on a 20% resist target.

For Lightning pen, the math gets even more complicated. lets still do the 7000 lightning and 3000 cold+fire split. but now, the target has 20% resists, so we multiply our lightning damage with 1.17 instead (instead of lightning pens actual value, 1.37). 7000 x 1.17 = 8190. Then, we do the same for our cold+fire damage, but they do not have penetration, leaving us with a 0.8 multiplyer. 3000 x 0.8 = 2400. now add those two numbers together, giving us 10 590 damage.

So in total, on a 0% resist target, our damage will be 13 000 with iron will, and 12 590 with LP.
On a target with 20% resists, we will do 10 400 damage with iron will, and 10 590 with LP

From this point on, the more resist your target gets, the more benefit you will get from lightning pen. This is why Lightning pen is my personal preference. You deal nearly Identical damage with iron will to low resist targets, but once you targets start to get resists, lightning pen pulls ahead by a lot. Keep in mind, this example is for my own build spesifically. Your own numbers might be different. if you have Less spell damage than i do from other sources, Iron will might be a lot more powerfull for you.

I do hope this clarified this a bit, and i hope you will be able to find your own numbers and calculate wich choice will be best for you!