Thought Impending Doom was cool, but had a Pathfinder leveled, and wanted to try a different take on it with poison prolif. This is where the build ended up. By no means fully min/maxed, but it was very comfortable mapping, and despite the low HP, was incredibly tanky. Huge movespeed and DoT playstyle also makes it amazing for Sanctum. I've been experimenting with some other builds, so wanted to leave this here in case anyone wanted to try a PF version as well.

https://pobb.in/LfdO56zYl55a

TLDR: Curse immune, Full ailment immune, tons of recovery, permanent flasks, Master Surgeon/Flagellant recovery, good DOT damage, Poison Prolif for clearing, high effective hit pool (phys is weak still)

Note - PoB doesn't really support Impending Doom properly, the cast rate shows up as a fraction of the curse applying it for whatever reason, which tanks the listed DPS. I grabbed some custom modifiers from Ruetoo's PoB to fix that, though I'm not certain they're accurate. Calculating accurate DPS between overlaps and chaining prolifs is probably not realistically possible, but you can at least get an idea.

Pros:

Pathfinder Tank - perma elemental flasks paired with master surgeon and Flagellant mod and stacking charges gained, means you're recovering 20%+ of your life when you're hit. Flasks also releive some gear pressure on resists, and you can solve things like stun immunity, curse immunity or mana costs with flask suffixes.

Poison Prolif - Works similar to profane bloom on occultist, and with enough packsize/ in the right maps, it can clear screens ahead of you. It lacks the explosion, so it feels different, but it is quite impactful. I wanted to test Low Tolerance stacking, but was having a hard time fitting everything.

Huge Movement Speed - permanent quicksilver with lots of flask effect makes this build zoomy and great for Sanctum.

Cons:

Wither is harder to maintain than occultist, who gets it automatically. Wither totem does also significantly reduce movespeed, which on top of high effect Temporal Chains makes most bosses a joke. But this costs gem slots that Occultist can free for other things.

Occultist gets more damage (-chaos resistance node), and a bit more curse effect, though only 10%.

No Profane Bloom. You could use unspeakable gifts clusters, or drop apep's for obliteration but I wouldn't recommend it.

Things I'd improve:

Phys mitigation is still low. Swapping a more defensive chest for Cospri's would help with that, though it would cost you some skill points to get another curse, and fix up poison chance.

2x Awakened Spell Cascade - gives you a 3rd overlap, stacking poisons ~50% faster.

52% CDR breakpoint - This would likely require 25% Balance of Terror Jewel, Belt and Boot mod (high tier eldritch implicit could work). Possible that you need this once using Awakened Cascade to keep up Impending Doom charges.

Paak's FAQ

In case you're unfamiliar with the mechanics behind how this setup works, I'd recommend reading Paak_HC's FAQ, he did a lot of ID mechanics testing on the Occultist version- https://docs.google.com/document/d/19-YNfsUeCNNmq0PjkHr-UMt-ILjE34SAXMlUs9QAi2g/edit#

Let me know if you try it, and if you've found some improvements I didn't mention.