[3.8] Winter Orb Poison (?) Assassin - All Content up to Uber Elder/Off-meta Build

Lair of the Hydra & The Constrictor
Uber Elder

Normally, poison builds suffer from two issues. One is sustain since you can't leech from posion damage. Sustain is not an issue in T15 maps or lower, because life flasks are enough there. However, once you enter T16 maps, you'll realize the sustain problem.
The other issue is clear speed because poison is a stacking DoT. Poison can deal a lot of damage when you apply a lot of stacks on your target, but you lack burst damage that is necessary to kill packs quickly.

This build solves these issues by using hit damage. In contrast to most poison builds, this build has relatively high hit damage to kill mobs quickly. We also uses Herald of Ice to help us to clear mobs. Because our hit damage is high, we can also leech life. Our hit damage is not enough to kill rare/unique enemies, so we rely on poison damage to kill them.

Winter orb is a great skill for poison builds because multiple projectiles from the same cast can hit the same target (shotgun). Also, the "less projectile damage" mod of Greater multiple projectiles support (GMP) doesn't affect our poison damage, because poison is not "projectile". Thus, we can use GMP as a "500% more poison damage" support as long as all the projectile hit a single target.

Mods that scales both hit and poison damage (Highest priority)
-Increased damage
-Increased cold damage
-Add x cold damage (to spells)
-Add x chaos damage (to spells)
-Gain xx% of elemental damage as extra chaos damage
-Gain xx% of non-chaos damage as extra chaos damage
-Increased chaos damage (once you gain "extra chaos damage")

Mods that scales only poison damage
-Increased poison damage
-Increased damage over time
-Increased damage over time multiplier
-Increased chaos damage over time multiplier

Mods that scales only hit damage (Lowest priority, don't take these)
-Increased spell damage
-Increased projectile damage
-Increased area damage

These three uniques are essential. Corrupted mods are not mandatory, and you have several choices. For Watcher's Eye, look for at least one of the Vitality mods.
Icefang Orbit enables us to shatter enemies and proc Herald of Ice.

Other items:

Note that empower support is optional; use it if you have trouble spending your exalts. If you cannot afford level 4 enlighten, drop Malevolence and use herald of agony.

Minimum requirement:
Weapon: Scepters with "elemental damage as extra chaos damage" and crafted cold damage/chance to freeze. Note that scepters can't roll chaos damage over time mod.
Crafting Guide

Body Armour: 6-linked and decent life.
Helmet: Decent life and resists.
Boots: Temple mod (30%MS and chance to dodge attack or spell hits), some life and resists.
Belt: Life and resists.
Ring: Life and resists. Crafted -3 mana cost.
Amulet: Non-chaos damage as extra chaos damage and life. Crafted -3 mana cost.
Anointment: Whispers of Doom if you have temp chain corruption on gloves, otherwise Hunter's Gambit (damage) or Constitution (life). Cheaper option is Corruption

Jewels:

"Corrupted blood cannot be inflicted on you" is highly recommended. Unique jewels are optional. Brutal Restraint can grant you "gain onslaught on kill". Use divine orbs until you find this mod. For the position of these jewels, see my PoB link (Passive Tree Section)

Flasks

If you don't have "Despair on hit" sceptre, use Witchfire Brew instead of Dying Sun.

Ascendancy points

Crit sucks for poison. Don't take it.

Level 95 Passive Tree

PoB link https://pastebin.com/yLLp68pt

Kill all
Soul of Lunaris/Soul of Shakari

Start with blight, then Bane. At level 43 you can eqiup the unique gloves and start poison Winter Orb.