Here are the best Skill Gems & Passive Tree for the Poison Blade Vortex Occultist Build. that includes the Skill Tree Progression for Leveling, Midgame and Endgame.
Poisonous Concoction Setup
Poisonous Concoction is your main ability until the Blade Vortex swap. This skill gem can hit multiple targets with its overlapping AOE projectiles, so link Greater Multiple Projectiles Support and Greater Volley Support. Void Manipulation Support and Deadly Ailments Support provide damage, with Unbound Ailments Support providing additional damage and duration of ailments.
Your primary movement ability is Shield Charge linked to Faster Attacks Support. Use Flame Dash to traverse over gaps or dodge dangerous boss abilities when necessary.
Use Determination linked with Divine Blessing Support to mitigate Physical Damage. This Aura buff expires approximately once every 20 seconds, make sure to re-cast it before it does. Use Grace to obtain Evasion Rating, giving you Chance to Evade Attacks.
Plague Bearer + Withering Step
Link Plague Bearer and Withering Step to Increased Area of Effect Support. Plague Bearer is your main Map clear ability that you load up and activate once it is done incubating to damage nearby enemies. Withering Step is how you quickly apply 15 Wither debuffs, causing enemies to take 6% increased Chaos Damage per Wither stack.
Blasphemy Support linked with Despair turns your Curse into an Area of Effect Aura. This pairs very well with Profane Bloom giving you an easier way to access explosions. This is later swapped for Temporal Chains once you equip Temporal Chains with Despair slotted in it.
Cast when Damage Taken
Cast when Damage Taken Support linked to Molten Shell triggers a shield that scales off your Armour and absorbs damage for a duration. If you can't use Determination to scale your Armour yet, replace it with Steelskin.
Once you obtain everything needed to perform the Blade Vortex swap as detailed in the milestones, change your main ability to Blade Vortex. Link Blade Vortex to Unbound Ailments Support for Poison Duration and Damage, Unleash Support to greatly help with sustaining 10 blades, Deadly Ailments Support to greatly boost our damage and eliminate the risk of dying to Physical Reflect, Efficacy Support to make blades last longer as well as providing more damage and finally Void Manipulation Support for raw damage.
Passive Tree Progression
Blade Vortex Swap
Before Swapping to Blade Vortex make sure to have crafted EVERYTHING from Milestones 6-8 in Early Game. Once completed you are ready to make the swap to Blade Vortex. This means you should have a level 80+ character, otherwise keep farming maps until you do. Make sure your resistances are capped and that you have enough Strength to use Determination, as well as the Increased Mana Reservation Efficiency needed to reserve your Blasphemy Support Curses and your Auras.