Level 90 Herald of Agony Herald^{3.25.alternate}

Notes

Leveling: 
I'm planning on SRS to Library -> Swap to HoAG when enough links for HoAG (pref 4 link) + Herald of Purity (3+ Link) + quill rain. You really need the quill rain for the Attackspeed + mana on hit to sustain the virulence stacks, otherwise keep leveling with minions (mainly srs).
Won't be the fastest leveling ever, but after the bow swap it should be OK.

Rain of arrows as main skill before swapping to storm rain with GMP

This build benefits extemely from doing early heist for ~50-100c (chaos recepe) to get all the uniques setup and enough chaos to craft yourself the 4/6 medium clusters. (alt spam until you get pure agony). Each cluster is 17% more damage.

Grabing alira during acts makes gearing for dex a lot more comfy in early maps. Lategame swap to +1 skillpoint.

Ascendencies:
1. Mana reserve (cant get anything else). !!! you can delay this to still use auras if you want !!! After you click this, make sure to get arctic armor + double herald 4l setup
2. Herald of agony Buff effect (chaos res is kinda useless, but double poison chance helps sustain stacks a lot, since no poison chance near start and no reflect jewel yet)
	Could go Herald of Purity effect here if u feel too squishy, but since ur a bow character, just dodge
3. +25 Virulence -> this is the omega spike, 80% more dmg node here -> really want to make sure u have ur skills setups correct here for manaforged triggers.
4. +3 Herald Levels


Item Progression in terms of item priority:
1. Quill rain (during acts with ur first chaos)
2. Thiefs torment - very important for sustain - pref during acts
3. Rearguard/Hyrri's Bite, not high prio if expensive
4. Rainbowstride (if 1c), good defensive pickup combined with Rearguard. - Can click glancing blows at this point, nearly block capped + thief's torment sustains glancing blows
5. Golden Rule - this will probably be ~10c - only really needed for single target, if you get it, try to buy a corrupted rearguard that removes the phys implicit to lower the selfdamage. Should be automatically chaos res capped with ascendency + 100 poison stacks.
6. +1 amulet - get any +1 all/phys/chaos and craft life on it.
7. Lioneye's chest -> this gives u a free link for ur HoAG + very high armor for early PDR
8. Widowhail - u really want a 5 link to be able to fit faster attacks or momentum since ur losing the attackspeed from quill rain, aim for 230%+ (just increases block chance)
8a) Upgrade your rearguard to one with better block rolls + corruption to remove implicit
9. Calamitous Jewel, could be expensive, but very good for stack sustain with 20% ice poison chance + 25% more dmg. if too expensive just skip until later.
10. Aspect of the Crab beast - Because u have so much free mana, this is very good for PDR since with widowhail you will be at block cap, so ur stack uptime will be quite good.

Other Notes:
Before you drop thiefs torment you need to get elreon crafts on 2x ring to sustain mana and you need a mana on hit jewel.
During leveling after getting thiefs grip + first ascendency you can click MoM since you have tons of free mana (only HoAG + arctic armor are reserved) and a lot of mana sustain from quillrain + thiefs grip.
Don't spend your town gold too much, you will need to respec quite a few points from early leveling -> lvl 70 tree and then again when at ~85 to swap to triple cluster.
If you don't have lioneyes chest you need pierce in your links for clear.
Because of the ED effect you can use effects that read like "while at maximum x charges gain y". This is very good for the small cluster node for spellblock (10% spellblock unconditionally) to fix your block chance.
If you are dying to reflected poison: Get a corrupted rearguard so the implicit added phys dmg is gone. Make sure chance to poison support is level 1. If you do everything correctly you should only be taking roughly 60 damage per second from your self poison at 100 stacks.
For all of the leveling trees: feel free to spec all 3 +30 dex nodes if you need them.
Make sure u didn't click the poison pantheon or golden rule doesn't work.
Transitioning to voices: I think even 7p voices could be worth getting day 1 if they are under 10c and you are roughly lvl 90. Otherwise I'd say just go 4th cluster with a normal cluster if you have high enough level.
Ailment Immunity via Stormshroud in lategame with boot implicit + 2x abyss jewel (or essence boots + 1 jewel)
If HoAG gets stuck too much, can drop the hextouch curse setup to go automation + convocation + molten shell + selfcast curse. (or annoint sth else if you cba)
Tattoo 1x Bleed chance to get free 40% inc armor
If you want to run blink arrow -> Run 1x unset ring in most setups. Some can fit it without running an unset ring.

Herald of Agony scaling:
HoAG is a very special skill, because there are (nearly) no outside factors on gear that can increase its dps.
HoAG gets increased damage (additive with minion damage on tree/gear)
HoAG gets increased attack speed (additive with minion attack speed on tree/gear)
HoAG gets flat physical damage (additive with flat added support gems/auras)

This means that there are only 2 ways to scale HoAG: Gem Levels and Virulence stacks.
Gem Levels are pretty straight forward: Empower + Woke Gems + Replica Dragonfang + Corruptions on chest. Higher level on HoAG also increases its scaling from the above 3 per virulence stack.
Virulence is +25 from ascendency and then +45/60 from 9/12 cluster jewels in lategame + some additional from quality ending up with 137 virulence with Ashes and 4 voices.

"But virulence will decay so fast, you can never sustain": Virulence decay is capped at server tickrate (30/second) so technically you only need to apply 31 poisons per second to eventually cap/counteract the decay. 
The build however hits way more often, as on single target you have 27 hits from RoA triggers and 100 storm rain arrows in the ground triggering every 0.4 sec with 6 beams per arrow giving good coverage.