Hello, i'm not a content creator or any sort of expert, and as mentioned, i don't really see this as a guide, even though it got a bit guide-ish. I'm doing this as a "i wish someone did something similar when i started this build" sort of thing.

Disclaimer: i'm not saying this is a great build, and i'm not trying to claim or convince anyone of that. It's an okay, functional build at least from what i could experience. The reasons to play this boils down to "i just want to". I had fun with it, maybe someone out there will too, and i hope this helps. I league started with this in Archnemesis.

Pretty much every guide i could find is outdated in some way. There's this one at PoE Vault, but i noticed some weird stuff that made me wary of it - it allocates lone messenger but also claims to activate aspect of spider and defiance banner; it also checks unholy might but you're not gonna have that for single target; it also allocates soul of Shakari but puts 25 in "# of poison on you"; and it considers you're lvl99. Zizaran has one with realistic HC numbers, but it was made back in Ultimatum, so it could use a review. Odealo has another guide but it has similar issues to the one from PoE Vault.

EDIT: banners are still auras, so lone messenger does block them. Aspects can be activated even with lone messenger, though.

I gathered what made sense from these and tried my best to make a more updated version of the build, with more recent ideas. This is my PoB with the current state of my character. I checked some boxes and put some values in the configuration tab but i promise you that those are realistic numbers. I did my best but i'll admit there's still plenty of space for optmization, so i'll appreciate any input.

The skill: herald of agony is an aura that gives you 20% chance to poison on hit, 10% more damage with poison and, whenever you poison something, you get a virulence stack, with a default maximum of 40 stacks. For as long as you have any virulence stacks, you'll be accompanied by the Agony Crawler, which is how you actually deal damage - yes, it's a minion build. The Agony Crawler is invulnerable and can't be targeted by enemies, so it's great if you hate having your minions dying - but it can't taunt and pull aggro, in return.

Priorities for damage scaling: #1 - gem levels. #2 - virulence stacks (upkeep rate and maximum). Then you go for minion attack speed, minion damage and a little bit of minion accuracy.

Each virulence stack gives your agony crawler % increased attack speed, % increased phys damage and flat phys damage. Each gem level increases the values of these, so you definitely want as many gem levels as you can get.

Increasing the maximum stack count is also important but there's a caveat: realistically, it's really damn hard to keep it consistently high in normal conditions, specially against single target/bosses. The more virulence stacks you have, the faster you lose them. Once you get to 40, you'll be down to 20-30 before you finish blinking if you're not hitting something during that.

Consequently, having 100% chance to poison on hit is very important. The skill itself gives you 20%; you can get another 20% with a divergent quality HoAg gem; you get 40% from chance to poison support. Options to get the remaining 20%:

• Lone Messenger keystone from the calamitous vision cluster jewel will give you 50% more effect of buffs from your herald skill, which gives you extra 20% chance to poison on hit if you have a divergent HoAg gem.
• Since Siege of the Atlas, you can get [chance to poison on hit] as an implicit modifier on gloves from the Eater of Worlds.
• With an Ashes of the Stars, you can almost get 100% chance to poison with a divergent HoAg alone. Coupled with lone messenger's more effect of herald buffs, you won't even need a chance to poison support gem.

Cyclone vs Storm Brand: cyclone hits more times per second; if you want, you can get [chance to poison support] as a modifier in Elder-influenced gloves, which lets you link cyclone with cast while channeling support and ball lightning for even more hits per second - but keep in mind that you won't be able to get [chance to poison on hit] as an eldritch implicit modifier this way; the "problem" is you'll have to be melee, though. Which is the advantage of storm brand over cyclone. Linked with faster casting support and with the Runebinder keystone allocated, storm brand is perfectly capable of keeping your virulence stack count at 40+ even during bossing. You can setup a hungry loop for your poisoning skill to free some sockets (unless you want to use the cast while channeling setup).

I have plans of testing self-cast ball lightning as an extra alternative.

Just saw Velyna's take with storm rain, sounds interesting. I'll maybe give it a try sometime in the future.

Q: Any mandatory uniques?

Technically speaking, no. There are some uniques that do add a lot of quality of life to the build, though.

1. The Golden Rule (viridian jewel). It reflects any poison you apply back to you, stacking while you have less than 100 poisons on yourself. Congratulations, you just doubled your virulence stack gain rate. I'm not sure if soul of Shakari blocks any virulence stack you would gain from the blocked poison stacks, but i wouldn't recommend allocating it anyway. Don't worry about the poison damage - it is based off your hit damage dealt by your own hands (not your minions) so it should be negligible.
2. Lioneye's Vision. Pierce support immensely improves the agony crawler's clear capability, making this arguably BiS.
3. Cold Iron Point. +3 gem levels is just too hard to argue against. As an alternative you could craft +2 rare weapons instead. Zizaran's guide suggests a stabilising sceptre, which can be obtained in heists, and has a crafting guide in the notes of his PoB that should still work.
4. Circle of Nostalgia. You'll most probably need at least one of this, with increased agony crawler damage and increased reservation efficiency.

Important note about Glorious Vanity for Divine Flesh: you can commonly find people inserting a glorious vanity at the jewel socket near the Eternal Youth keystone. The potential problem with this is that it will also disable the gravepact cluster, which is one of the very few sources of minion accuracy in the passive tree. If you don't take it, you'll need to roll minion accuracy in ghastly eye jewels and/or take the longer route in the spiritual command cluster and/or take the minion offence mastery. The agony crawler has naturally high accuracy by default, but not enough to get 100% hit chance at higher monster levels. Resolute Technique does not affect your minions.

Also keep in mind that this build struggles really hard to cap elemental resistances, getting chaos resistance - so you can better take advantage of divine flesh - is even harder. Don't rely on the golden rule to cap your chaos res.

Gems: while herald of agony is regarded as the chaos/poison herald, void manipulation support is not an optimal gem. The agony crawler's damage is originally physical, while it has a natural conversion of 40% phys to chaos. There are better options to increase its damage as a whole, instead of less than half a portion.

The agony crawler is not the faster damage dealer, so you might want to carry frost bomb around for situations against enemies with strong regen capabilities - bosses being watched by Maven, mobs with the archnemesis' rejuvenating mod.

Stone golem gives us more regen and can be used to get feeding frenzy. If you opt for using cyclone, it might be better to use summon holy relic instead - it can be linked with withering touch support, which will increase your damage considerably. It doesn't work too well with stone golem because the golem doesn't attack fast enough to stack wither; and holy relic doesn't work with storm brand because it only releases the damaging nova if you hit with attacks.

Builds' biggest struggles: this build struggles really hard with resistances and attributes. You'll need a lot of dexterity and intelligence, to a degree too hard to get just in the passive tree. Consequently it gets harder to cap resistances because both res and attributes are suffixes.

• A workaround to this is to use the forbidden flesh + flame combo to "anoint" [Tasalio, Cleansing Water] from the chieftain ascendancy tree. This gives you +100% fire resistance, which means you'll only need one single high rolled fire resistance modifier in any item to cap your fire res, greatly alleviating the res capping + attribute hunt issue.

Playing without convocation feels really bad. The agony crawler has pretty long range, which should be a good thing, but this leads his AI to being left behind and loving staying behind walls and obstacles while still trying to hit enemies. Thanks to how its projectiles spread, it often leads to situations where it thinks it can hit an enemy but in practice it doesn't. Also proximity shields are a nightmare. Use convocation.

One of the juggernaut's biggest weaknesses is shock; i'm not sure and can't really explain why, but it feels like the shock ailment really messes up with how the damage you take is calculated. Soul of Garukhan is a good pantheon for this. You could also consider squeezing tempest shield somewhere in your build.