Normally Chieftain Ascendancy notable "Valako, Storm's embrace" is used as a substitute for Melding of the flesh, allowing the player to raise their maximum elemental resistances without the costly penalties associated with melding (70-80% reduced ele res and -4 max res). Less known is that Melding and Valako's work together and doubling typical sources of maximum resistances such as Purity auras, eldritch implicits on gloves/boots/helm and most importantly the newly changed elemental flasks. It is now possible to achieve 90 max res transcendence with Eternal Damnation (it was possible before but very costly) and full physical to elemental damage taken as conversion with little passive skill tree investment. With a 2x phys taken as watchers jewel (of which there are 14 usable varieties) it is even possible to use two-handed weapons or unique helmets while still achieving 90 maximum resistances. If you've never played a 90 max res transcendence build, with as little 50-75k armour you can tank almost every ability in the game

Let's go over the basic concept and why it's so strong:

Valako, Storm's Embrace:
Modifiers to Maximum Fire Resistance also apply to Maximum Cold and Lightning Resistances

Melding of the flesh:
Elemental resistances are capped by your highest Maximum Elemental Resistance instead

Notice that melding of the flesh sets your maximum resistance to your highest, while Valako's increases maximum cold and lightning resistances based on maximum fire resistance. Where this becomes interesting is if you have sources of maximum fire resistance and maximum cold or lightning resistance (you'll have to pick one). For example:

If you +7 maximum fire resistance and + 7 maximum cold resistance and nothing else, then your maximum resistances with Valako's will be: 75/75/75 - > 82/89/82.

Now if you add Melding, your maximum resistance is reduced by 4 82/89/82 - > 78/85/78
which is then set to your highest maximum resistance which is cold: 78/85/78 - > 85/85/85

At low maximum resistance investment it is hardly worth using melding, as in this case it only raised our maximum resistances by 3 compared to a regular chieftain with just Valako's. However, we can use them to offset the very powerful defenses of:

Eternal Damnation:
-5% to all maximum Resistances
Gain additional Elemental Damage Reduction equal to half your Chaos Resistance

Transcendence:
-15% to all maximum Elemental Resistances
Armour applies to Fire, Cold and Lightning Damage taken from Hits instead of Physical Damage

These two modifiers are additive sources of elemental damage reduction as I have explained in detail in a previous post: https://www.reddit.com/r/PathOfExileBuilds/comments/zqz6uj/the_eternal_damnation_and_why_its_so_efficient_on/ and can be used to easily achieve 90% damage reduction from elemental hits which is multiplicative with resistances. Unfortunately, this combo comes at the cost of -20% max res which you could either offset with Loreweave or invest in a LOT of increased aura effect, max res tattoos or wildwood charms (which are no longer available) or stacking maximum resistance sources on gear and the passive skill tree.

What changed this patch to make Chieftain so strong?

In patch 3.24, Elemental flasks were changed from giving "20% less X damage taken" to "+5% maximum X resistance", a massive nerf to high end pathfinder builds which stacked flask effect to achieve upwards of 60% less elemental damage taken. For pathfinder transcendence builds it was either a nerf or a buff depending on what your maximum resistance was, but at 20% flask effect - > 1 max resistance their scaling with flask effect has been dramatically reduced.

What makes Chieftain so special is that with melding of the flesh they can benefit from a ruby flask AND a topaz or sapphire flask, whereas other classes only benefit from one, though you will either need a Mageblood or the new tides of time belt for 100% uptime. Let's compare the two below:

Mageblood:
I believe this to be the more powerful and versatile option as you do not need to invest in flask recovery/duration, though tides of time is not without its advantages. With mageblood you can enchant your flasks to have up to 95% flask effect or 9% (5% x 1.95) maximum resistances per flask max res. For chieftain this is +18 maximum elemental resistances for 2 flask slots; a ruby and either a sapphire or topaz flask. Furthermore, since this is a transcendence build with 100% phys to ele dmg taken conversion, a basalt flask is extremely efficient as a third flask slot as all of our damage taken is mitigated by armour, with the fourth slot available for quicksilver, diamond, etc.

Tides of time:
With times of time you will need to invest in Natural Remedies and Careful conservationist notables (I recommend both as it lets you hit 140% flask effect for 7 max res) + some amount of Herbalist tattoos for 100% flask uptime which is a big passive skill investment, but you do get some nice spell suppression nodes on the way. Fortunately, elemental flasks have the highest uptime of any flask type so at bare minimum you can use all elemental flasks with minimal passive skill investment. The main advantage tides of time holds over mageblood is permanent uptime of Taste of hate which contributes to both your maximum resistance and your physical damage taken as elemental. This frees up a flask slot and means you don't need a dawnbreaker or an expensive two-mod watchers, though you will need to find extra sources of maximum resistance compared to mageblood (18 max ele res w/ mageblood vs 14 w/ tides of time). I would also recommend using multiple life flasks aka "Ben/Darkee style" as tides of time can provide both life flask charges and doubles life recovery.

So, how do we achieve 90 max res with transcendence and eternal damnation?

Let's assume 40% aura effect for a typical build (two aura clusters on the passive skill tree + aura buff mastery + aura effect militant faith)

Purity of Fire: 5 x 1.4 = 7 maximum fire resistance
Purity of Ice/Lightning 5 x 1.4 = 7 maximum cold/lightning resistance

Eldritch Eater implicit on boots = 2 maximum fire resistance
Eldritch Eater implicit on helmet/gloves = 2 maximum cold/lightning resistance

Mageblood (25% effect and atleast 55% effect enchant) w/Ruby flask = 9 maximum fire resistance
Mageblood w/ Topaz/Sapphire flask = 9 maximum cold/lightning resistance

7 + 7 + 2 + 2 + 9 + 9 = 36 max res from these three sources alone, with melding giving 14 (18-4) maximum resistances.

Total maximum resistance = 75 + 36 - 15 (transcendence) - 5(eternal damnation) - 4(melding) = 87 maximum resistances.

To get the extra 3 to reach 90 there are a variety of sources:
Prismatic skin cluster is right next to the chieftain start and gives 4 maximum resistances (2 max ele, + 1 fire, + 1 cold/lightning), but there are more expensive options if you don't want to waste precious skill points
Natural Remedies annoint = 2 max res with atleast a 65% flask enchant (25 + 65 + 10 = 100 flask effect)
20% increased aura effect e.g. Influence cluster = 2 max res
Reservation mastery or armour mastery (must be lightning coil) = 1 max res
+1 max res corruption on amulet body armour

If your build can use a shield then you can get 3-6 max res shield (technically it can go as high as 8 but this is almost impossible to craft). Aegis and Rise of the phoenix with Phys damage taken as X corruptions are a pretty good option.

The only difference with tides of time is that you will have 4 less maximum resistances, which means you will likely have to take the prismatic skin cluster on the way to taking the necessary flask nodes

So how much armour should I get?

What we really care about here is "What is the maximum elemental hit for which I have 90% elemental damage reduction?"

Here is the equation for calculating the elemental damage reduction w/ transcendence and eternal damnation (refer to my previous post for the derivation):

Ele_damage_reduction = min(Armour/(Armour + 5*(Ele_hit*(1-Ele_resistance/100))) + Chaos_resistance/200, 0.9)

Now the obvious place to start would be at 50,000 armour, which is where our molten shell caps out, the skill which allows us to tank everything. Substituting resistances 90/90/90/70, 50,000 armour and an elemental damage reduction of 0.9 (which means we can ignore min) we get :

0.9 = 50000(50000 + 5*(Elemental hit *(1-90/100))) + 70/200

Elemental hit = 81,818

Importantly, this isn't the same as the maximum elemental hit we can tank which can be much higher, it's just the maximum hit for which we have 90% elemental damage reduction, meaning for any hit below 82k we take 99% less damage from resistances (90%) and ele damage reduction (90%). Remember for hits above this value our damage reduction drops rapidly, so make sure to calculate first how much armour you need before tanking a boss slam in HC.

82k elemental hits in maps are exceptionally rare, it would require an extreme combination of mods in T17 for this to occur. For uber bossing this would protect you against all but eater, exarch slams, brain blast and maven fireball (penetration is especially effective against this buid. Funnily enough, you should be able to tank memory game at 50k as elemental damage of each type does not exceed 82k. For a softcore T17mapper + uber bosser I would definitely stick to 50k.

How much armour do I need to tank everything?

If we substitute 100k armour into our equation (which we can achieve using iron reflexes and grace as I will show in an example build) then the maximum elemental hit for which we have 90% elemental damage reduction is 163,636, which is definitely enough (although I haven't tested it yet) to tank maven fireball and eater of worlds slams and should be enough to tank brainblast based on the 150k damage hit per element estimates (don't quote me on this). Although you're probably better off capping your spell suppression if you don't care about exarch slam or brain blast. I don't know what the exact values for exarch slam are but I believe if you're directly under him you'll need a little bit over 100k armour.

For further analysis check out: https://www.reddit.com/r/pathofexile/comments/1abdujl/uber_boss_limit_testing_with_90_max_res/

Builds:

We've been working on a build using this concept since Week 2, unfortunately my friend who was putting the build together was pretty busy this month and ended up ripping today (HC), which is why I'm putting the guide out now.

Fortunately a korean player by account name "Solderist" also known as "Hoon" https://www.youtube.com/@Hoon_PoE also figured out the tech, using reap as his primary damage skill: https://poe.ninja/builds/necropolis/character/Solderist/Nec_Transcendence

Note that Hoon is able to achieve 90 max transcendence ED without needing the Prismatic skin cluster or the eldritch implicits on his boots or gloves, or corrupts on his amulet or body armour. Mageblood gives so much in maximum resistances and armour that he/she can invest relatively little in defenses on the passive skill tree.

Here's the guide to Hoon's build:
https://www.youtube.com/watch?v=m3UoJJBXUhg

Since no one has put together an equivalent tides of time build yet, here's the unfinished build we would've gone, and are putting together on standard. It's as budget as I could make it(for a build this tanky) HC Zenith flamewood build that should be able to tank everything and with a dps of ~20mil (I don't know how to make PoB accurately calculate flamewood Dps but it's roughly 28x the average hit if all totems are up and getting hit) https://pobb.in/mI9-MCLPsDvk. For HC the budget is around 100D right now, but for SC I'm pretty sure it's closer to 20-30D. I have been told these items are terrible for softcore standards, so you'd probably be able to make a much stronger build.

Build requirements:

If you want to make your own build, here are the mandatory items:
Mageblood or Tides of Time
Melding of the flesh jewel
Eternal Damnation
Lightning coil or Cloak of Flame
Militant Faith unique jewel (Maxarius)

Atleast 3x Herbalist tattoos or more if you're going Tides of time

Strongly recommended:
Rare helmet with 15-18% physical damage taken as elemental
Watcher's eye jewel with 1 or 2 physical damage taken as mods, of which there are two combinations. If you also use a purity of elements there are 12 further combinations for a total of 14 possible two mod watcher's jewels.
Dawnbreaker for mageblood if you can't afford a twin implicit watcher's or alternatively a +5 shield like aegis or rise of the phoenix with a physical to ele/chaos corruption

Cool combo for immortality
Valyrium, bloodnotch, immutable force tech, possibly with petrified blood should make you effectively immortal even in T17s.

What skills:

No matter what primary skill you'll want Purity of Fire, Determination, Molten shell and one of either Purity of Ice or Purity of Lightning. Grace with iron reflexes is a simple way to reach 100k armour, but not necessary.

For mageblood, with the exception of charge stacking and attribute stacking builds, any chieftain or marauder build with forbidden jewel Valako can use this defense tech. In fact I'd argue that this is the most efficient and versatile defense tech, requiring no aura or armour or flask effect stacking and the excess of maximum resistances means you go whatever skill passive skill tree you want (so long as you can get the watchers you need). Reasonable candidates for skills would be RF, non-trauma stacking melee builds, spells like reap, zenith flamewood and detonate dead.

For tides of time, since you're forced to invest into the right side of the passive skill tree you either want a highly efficient skill like flamewood zenith or skills that benefit from right side passives, like nimis projectile/poison skills. I usually don't go those kinds of builds, but I'm sure someone can make a cool tides of tide poison molten strike chieftain.

Closing statements:

Thanks to the flask changes this patch, achieving 90% max res transcendence w/ ED has never been easier for Chieftain in combination with melding of the flesh. The defense tech is highly flexible and efficient and can be used on most chieftain builds or marauder builds with valako's forbidden jewel. While the mageblood version is more versatile, budget versions using tides of time have their advantages and can be just as tanky. I'm not sure how this compares with the most expensive armour stackers or pathfinders with progenesis and flask effect stacking for deep delving (you could probably make a decent deep delver with aegis), but it's certainly far more flexible and cheaper and can still tank all uber abilities. I hope to see some cool builds using this tech, especially in conjunction with valyrium/bloodnotch.

Thanks to my friend TheTrashking for helping put the build together, even if we weren't able to complete in HC. Thanks to Hoon for the putting together a mageblood version and putting a build out, please go see his channel: https://www.youtube.com/@Hoon_PoE