Most people are aware that PConc Occultist is a S-tier mapping build, however when it comes to bossing the build is known not to perform that well, at least in a non-trade scenario. With the 3.20 buff to poison builds in general I wanted to see how the build performs nowadays from leaguestart to Uber bosses. I won't go into detail about the basics of a PConc build, there are plenty of guides already out there. Instead, I want to give some insight into the choices to make this build able to kill Ubers, although I certainly would not recommend this as a boss farmer.

TLDR:

All uber boss videos

General PoB: https://pobb.in/ghexdQ8sxzpz

I don't run Ancestral Protector because I consider this just PoB padding when we don't instant-phase bosses.

Divine Blessing Malevolence is generally more damage than Haste, but for some boss fights being able to react quicker (faster action speed, faster cast speed for Arcanist Brand) felt more important than raw damage, particularly for Uber Uber Elder.

Purity is changed depending on the boss fight; Exarch setup has a separate non-spell-suppression tree and drops Grace for Haste; Sirus setup uses Saffels and a CB jewel and drops both 50% auras and uses 3 purities.

Cortex is currently bugged and gets the 100% increased effect of modifiers twice (non-uber Cortex gets 100% increased effect always due to a bug, and then the uber Cortex keystone adds another 100%). I misplayed in the last phase, but in general I think this is only really solved with more dps; there's not much to outplay when the whole area is full of degen.

From all my SSF characters in the past year that did the very endgame this is probably the one with the worst gear. My rough PoB plan was something alike to this but I never got a shield with +all max res and +chaos max res (thanks Rog) or an amulet that has at least 2 damage stats. Some sockets should also be white for more efficient aura management for the different bosses. Nevertheless, the numbers looked good enough to tackle Ubers before christmas is coming up.

This was my mapping setup from 99 to 100 once I got diadem, but the non-diadem setup which used Devotos for most of the time was a lot more fun for mapping and sanctum just because of more movement and attack speed.

Detailed comments:

The basic bossing setup runs Diadem to get access to EB which allows to drop lifetap as a main link and also makes reservation easier without having to socket lifetap on supports; PConc is really socket starved due to not having a main-hand weapon, so every socket we can drop is valuable. With EB we lose out on one of the strongest (and with Malediction gone in 3.20 pretty much the only) defenses of early-game Occultist, which is Ghost Dance. The most important damage mitigation for Ubers is elemental damage, and my go to for Ubers on poison-based witches in the past year has been Xibaqua, mainly because early witch pathing sucks anyway and I consider the spot below Pain Attunement pretty much the only viable Glorious Vanity spot on the right side of the tree. Getting high max chaos res is also not too bad with a +2/+3 chaos shield, where Rog can really help.

An alternative I can see is not using diadem, keeping Ghost Dance and using Eternal Damnation (potentially with Loreweave), but with a good amulet that setup loses a lot of damage; given that my amulet really sucks it's an interesting option for sure.

Apart from Manni's Gucci Hobo week last league this is the first time I used Dendrobate for Ubers. It is a good offensive chest and also a good double corruption target since it's quite common. However, it has two drawbacks: 1) it requires some investment into dex and depending on pathing on int; 2) its main drawback is that the defensive stats are not particular strong, especially if you go EB and don't need the energy shield to activate Divine Blessing. The first point isn't that bad, since we get evasion and accuracy from dexterity and already get quite some dex from pathing. Nevertheless, a rare chest with + all max res and some spell suppression to free up passive points is most likely the stronger option overall.

I don't think that there is anything else that is particularly interesting that wasn't already covered somewhere else, most of it is basic PConc stuff. Perhaps the decision of whether leech is necessary compared to swapping Vicious Projectiles with Deadly Ailments. In the end I think this depends on the fight, particularly after watching the fights I think for some bosses leech is not really necessary, which would result in a lot more damage.