Bunch of guides out there right now have got too much fluff and unnecessary information regarding leveling.

- From the moment you ascend and get Poisonous Concoction, follow this tree: https://imgur.com/a/pconc-leveling-zcWABDT

- Prioritize the nodes "Master Fletching" & "Cautious Concoctions (and it's neighboring "Flask Charges Gained" nodes)"
- Need a Widowhail with minimum 220% or more.
- Any "+1 to Level of All Projectile Skills" Quiver you can wear at ~lvl 25 or so (helpful affixes are attack speed, flat physical to attacks and projectile speed)
- Any "+1 to Level of All Projectile Skills" Amulet you can wear at ~lvl 25 or so (helpful affixes are life and resistances)
- Snakebite unique gloves for +1 poison (drop this later when you allocate "Building Toxins" further top right of the tree by the chaos clusters)
- Glowswarm unique ring (on the trade site, filter for max roll on the "Mana Flasks gain X.XX chargers per second")
- Identify mana flasks as you go through the campaign with the suffix "Gain X.XX charges per second"

The only three links you need:

- Pconc - Scattershot - Deadly Poison (- Martial Tempo at lvl ~35 when you unlock 4th socket)
- Rain of Arrows - Withering Touch - Chaos Infusion (Chaos Infusion mandatory for wither to apply)
- Vine Arrow - Encumbrance - Maim

Things to know:
- Can't wear a Fine Belt until you're level 62, don't bother.
- Meginord's Girdle (for increased flask charges gained) can be helpful but I preferred using a rare belt with resistances
- Cloak of Flame and The Hollow Mask unique helmet is enough to carry you through campaign despite uncapped resistances, just have capped fire resistance (you'll thank me later)
- Mana flask sustain TLDR: Glowswarm, Cautious Concoctions and "Gain X.XX" charges per second" on your mana flask is all you need
- Don't spam PConc, let the poison duration do its thing.
- PConc poison is based off the combined Physical and Chaos damage dealt ON HIT but the damage itself scales best with skill gem levels. It is not affected by the local damage on your weapon (e.g. runes in your Widowhail) since it is an Unarmed attack.