The Vixen's Entrapment Unique allows you to automate Curse application, increasing quality of life, damage and survivability. Whispers of Doom and Vixen's Entrapment your Curse limit is set to 3, so if a 4th Curse is applied it will overwrite a Curse, forcing a Doom Blast to trigger. Because of this interaction you must be wary of how your gems are socketed into your Gloves. The Curse in the top left most socket is overwritten, and does not affect the monster, therefore you must choose between Punishment or Enfeeble depending on whether you want more damage or survivability. Once you have equipped Vixen's Entrapment you can re-spec your Unholy Authority Ascendancy to Vile Bastion as the gloves will allow you to apply an additional curse instead.

Divergent Herald of Agony provides additional global Chance to Poison. This is important because it enables you to save passive skills leading to Skittering Runes since you can now swap your amulet anointment to it. Make sure to adapt your passive skill tree once to the midgame variant once you do!

Suppression grants a % chance to reduce incoming spell damage of hits and their ailments by 50%. This caps at 100% to effectively half our Spell Damage taken. Your primary sources of suppression are: Body Armor, Boots, Gloves, Helmet, and Shield Suffixes. This stat can only roll on Evasion or hybrid Evasion bases which isn't a problem for this build. The easiest way to do this is to obtain a Supreme Spiked Shield and/or Dragonscale Gauntlets to use Harvest Reforge Life, Essences or craft with the Expedition NPC Rog until you've obtained 17%+ Chance to Suppress Spell Damage, and 70+ to maximum Life. A unique which can greatly help with capping Spell Suppression as well as Elemental Ailment Avoidance is the Elevore. It grants 20-25% chance to Suppress Spell Damage & 20-25% chance to Avoid Elemental Ailments as well as Recover 100-200 Life when you Suppress Spell Damage.

A 6-link rare armour is going to provide us with a defensive power spike in the mid game.

Make sure to only craft on a Battle Lamellar or General's Brigandine as they will provide you with the most amount of Armour and Evasion a Body Armour can provide.

The ideal Body Armour has the following stats:

Flasks are an extremely important part of our build's avoidance and mitigation, properly invest into them. You need these 3 mods on 3 Flasks.

Use the Flasks below, fitting the above mods onto 3 of them where available. Buy or roll Flasks for the mod x% increased Charge Recovery. Grab item level 70+ Utility Flask bases, rolling x% increased Charge Recovery should take about 30 Orb of Alteration each Flask, for 90 in total. Either Orb of Augmentation into those, or buy those mods on at least one if you have to.

Go to your crafting bench and craft Used when Charges reach full on your 3 Utility Flasks to automate their use. This will cost you 5 Instilling Orb and 5 Glassblower's Bauble each.

You should look into upgrading your second ring into a Death Rush if you wish to get more damage and speed for mapping (as the effects granted by the ring are on kill they do not apply to bossing). Note that the rolls on this ring has a high variance, when purchasing make sure to get a decent roll that is within your budget.

If you have a belt with T3+ Life, and 2+ Resistances/Strength then skip this step. Grab an item level 82 Stygian Vise. Harvest Reforge Life or Shrieking Essence of Rage until you obtain T3+ Life, and 40+ Strength with a Resistance. Finish it by crafting 9–12% increased Cooldown Recovery Rate in your Suffixes.

For your Abyss Jewel, grab one that has x% chance to gain Phasing for 4 seconds on Kill and one or more of the following modifiers:

Your Helmet and Boots can all have 2 Eldritch Implicits each. These Implicits can be added by applying Searing Exarch and Eater of Worlds currency.

Eldritch Currency is found from Altar Rewards in Maps after choosing either the Searing Exarch or Eater of Worlds Beacon on the Map Device. They have tiers, for example the lowest tier currencies are: Lesser Eldritch Ember and Lesser Eldritch Ichor. If you don't like an outcome, just roll over it with another Eldritch Currency. Don't go overboard on rerolling, you'll have to redo the Implicits later anyways.
Here are some good outcomes to remember:

Helmet:
Searing Exarch: #% increased Despair/Temporal Chains Curse Effect
Eater of Worlds: #% increased Duration of Ailments on Enemies

Your first Watcher's Eye mod should have:

If you can afford an extra modifier look for one of the following:

Look to upgrade your amulet to an The Eternal Struggle. This amulet is unique in that it has the potential to roll with one eldritch implicit modifier each of Eater of Worlds and Searing Exarch pools. The tier of the implicit (and therefore the dominance) is determined based on which boss dropped it. The Black Star generates an Exarch dominated variant while the Infinite Hunger generates an Eater dominated variant.

Items with Eldritch Implicits can also have a property of being dominated by one of the Eldritch Horrors. If an item has a higher-tier Searing Exarch mod then it is considered dominated by The Searing Exarch. Conversely, if the mod for The Eater of Worlds is higher tier, then it is considered dominated by The Eater of Worlds. It is really important to look for an amulet with Searing Exarch dominance as you want the following modifier be enabled: Kill Enemies that have 15% or lower Life on Hit if The Searing Exarch is dominant. To ensure the amulet you purchase has the correct dominance you must check the modifiers tier on the following list. As a final check, make sure to hold the alt key once you go to trade for the item before accepting the trade. This will give you an indication as to which modifier is of a higher tier, and guarantee that you are purchasing an amulet with the correct dominance. For reference the tiers go in the following order: lesser -> greater -> grand-> exceptional -> exquisite -> perfect. You can also use this trade search as it filters for the best modifiers as well as the correct dominance.

Here are some Searing Exarch modifiers to look for:

Here are some Eater of World modifiers to look for:

The The Balance of Terror is a jewel that drops from the final boss in the Forbidden Sanctum. It comes with 2 random modifiers, one of which grants 20-25% Cooldown Recovery Rate if you've cast Temporal Chains in the last 10 seconds. This Cooldown Recovery Rate translates to a significant 20% or more increase in DPS. Once you acquire and equip this jewel, ensure that Temporal Chains is included in your main 6-link setup, as the bonus won't apply if it's triggered by Vixen's Entrapment.

At this point, we are moving into big and expensive endgame upgrades, so make sure you don't have any gear pieces that could be easily upgraded. Resistance Caps, Spell Suppression should be second nature to you at this point and should be checked after you shuffle your gear around!

The easiest upgrade you can make is going to be Awakened Gems and Alternate Qualities. Purchase the following Awakened Gems:

Purchase the following Alternate Quality Gems:

Purchase the following Exceptional Gems:

Skin of the Lords is an extremely powerful Unique Armour because it gives 100% Increased Global Defences, +2 to Level of Socketed Gems and a Unique modifier granting you a Keystone. Global Defences scale your Evasion , Armour, and Energy Shield making this unique very efficient for scaling your defensive layers. The +2 to Level of Socketed Gems modifier boost your damage substantially when you socket Impending Doom Support into it.

The best keystones to look for when searching for this Armour on trade are:

Keystones you MUST AVOID:

IMPORTANT: You cannot modify the colours onSkin of the Lords; It must be purchased with the correct Gem colours. It also only allows for corrupted gems to be socketed within in, so you have to corrupt all your Skill and Support gems.

As the Skin of the Lords Body armour can be rare and expensive to find with the correct socket colours, you can consider to following body armours with an implicit corruption as suitable alternatives until you can afford one:

Suitable Corruption Implicits:

Atziri's Reflection is a great shield for this build as it provides up to 20% increased effect of your Curses. This stat is one of the best way to scale both your survivability and damage. The shield also provides a ton of Energy Shield and Elemental Resistances as well as making your character unaffected by Curses. This means that you don't have to worry about map curse modifiers or monsters inflicting them as they will have no negative effect on your character.

The helmet slot is going to provide you with a massive amount of Curse Effect which translates to a ton of additional damage. It also is the only place where you can get the 61-70% increased Duration of Ailments you inflict while Focused modifier. This mod allows you to make use of the focus skill, a very strong cooldown you can use on tanky monsters or bosses to granting a huge boost in single target damage.

The most important prefixes on our Helmet are:

The most important suffixes on our Helmet are:

The most important eldritch implicits on helmets are:

The most important Lab enchant is:

Thanks to Eldritch implicits and the Deafening Essence of Torment we can beyond to 100%% chance to Avoid Being Shocked on our Boots. This enables us to be fully ailment immune with the Stormshroud jewel It is difficult to land good suffixes by spamming Essences, therefore make sure to purchase a pair with a fractured resistance.

The belt is a great place to get the strength needed to equip all of your red Skill Gems, as well as a ton of additional Cooldown Recovery Rate. The Cooldown Recovery rate is a stat which provides a ton of damage as it allows Impending Doom to trigger on more casts. This craft can be expensive so make sure that before you begin crafting, you check on the trade website whether there is one that will suit your build and satisfy your resistance and attribute requirements.

We use this slot to fill out as much of the stats that we are missing as possible. This makes this slot unique to your current setup as that might change depending on the stats you have on your other items. The best way to fill this slot is to look for a combination of the stats you are currently missing on the Trade website, as crafting with Essences most likely costs way more than one you can find there. Try look for a ring with 3 good suffixes, then you can craft life and use it as is, or craft Suffixes Cannot be Changed, scour and craft Suffixes Cannot be Changed before using a Veiled Chaos Orb. Block +# to Maximum Mana before unveiling Life, finally craft % increased Damage to finish the ring. Look for a combination of the following suffixes on a ring while keeping in mind the build has many available Jewel Sockets where you can also fill out remaining resistance and Attribute requirements:

Watcher's Eye

The Watcher's Eye can grant a boost to both your defenses and offenses. Since this build utilises two defensive, and one offensive aura there is a wide range of stats we can look for on it. Look for a jewel with the % chance to Suppress Spell Damage while affected by Grace and if possible an additional mod listed below:

Stormshroud

The Stormshroud Unique Jewel is an essential part of your defenses, It allows you to stack % chance to Avoid being Shocked instead of % chance to Avoid Elemental Ailments. This is beneficial because it is a much more easily accessible stat which can be rolled on Boots to grant you full Ailment immunity.

Rare Jewels

Cluster Jewel

You've reached the end of our Milestones, congratulations!

Every upgrade beyond this point is not simple enough to serve you in a static format like this. This is because most of your upgrades going forward will heavily depend on the choices you made. However, that doesn't mean that your journey ends here. If you want to go further, check out other people's versions of the build on poe.ninja. They give great insights and new creative ideas!