Level 99 Toxic Rain Pathfinder^3.23

Notes

-What Cluster Jewels Should I Use?
Large Chaos Damage Cluster Jewels with 8 mods. The preferred notables are Unholy Grace, Unwaveringly Evil, and Wicked Pall.

Medium Projectile Damage Cluster Jewels with Shrieking Bolts and Repeater is ideal for maximizing damage.

Medium Chaos Damage Over Time Cluster Jewels with Wicked Pall and Student of Decay is a good alternative that can help with Chaos Resistance. The difference in damage is pretty small.

-Is the Thread of Hope necessary?
No, but it is a good endgame optimization that lets you anoint Sovereignty without losing the massive damage from Potency of Will.

-Do you need a Despair curse-on-hit ring?
No, but it's convenient! Many players self-cast Despair on rares and bosses, but that's tedious.

-Do I need Forbidden Flesh/Flame?
Hell no! They're a super expensive flex, and a really bad investment that dropped in price by ~50% within a week of when I bought them.
They do make me zoom fast, though, so I am not complaining!

-What Watcher's Eye mods should I use?
Phasing while Haste is active is pretty good, and surprisingly cheap. You can get Phasing elsewhere, but this is a really easy spot for it.
Phys Taken as Light/Cold/Fire is massive for increasing your tankiness.
Increased Damage Over Time Multiplier While Affected By Malevolence adds a ton of damage, which is great, but it is insanely expensive with the other mods, and can push you over the DoT cap. Not a priority.

-Why not Headhunter?
Consistency! Mageblood makes trivializing mana pretty easy, and it makes you consistently zoomy!

-Why not Defiance of Destiny?
Damage! I spent ~4000 Orbs of Alteration crafting this +2 neck, and I'm going to enjoy the ~25% more damage it grants.
Defiance of Destiny is a great alternative, it will make you UNREASONABLY tanky, it just comes at the expense of some damage.

-Why not all 3 Ele Res Flasks?
Same reason! It's a super-tanky setup, works great, but you have to give up some damage & speed for it!

-What about Taste of Hate?
It's an excellent budget alternative to Progenesis.

-Do I really need to use a Life Flask?
Defiance of Destiny can work as a pretty good substitute, but you will need to account for DoT effects, and find another way to deal with Bleed & Corrupted Blood.
Corrupted Blood immunity through Corrupted Jewels will work, but for Bleeds you will probably want to run Steelskin instead of Immortal Call, and switch to Ralakesh for your Minor Pantheon.

-Do I need these specific Charms/Jewels?
Nope! Charms, Jewels, and Rare gear are all about solving problems. You need a certain amount of resistances, stats, and spell suppression to make the build function safely.
Acquire them across all those pieces of gear as you are able.

-How do I fix mana?
During League Start, a mana flask or Eldritch Battery will work, but at endgame, a 25% Reduced Mana Cost of Skills crafted Flask suffix is extremely important.
With a Mageblood, that's basically all you need. One flat -Mana Cost of Non-Channeling Skills craft on a ring will get your TR casts down to 1 mana, which is crucial for triggering Manaforged Arrows.

Without Mageblood, Increased Flask Effect in the tree and a couple of jewels or rings with % Reduced Mana Cost of Skills will work.

Be sure to link your Divine Blessing to Inspiration Support (and +20% Quality the Inspiration Support) for the reduced mana cost it provides.

Note: If you use Eldritch Battery, Manaforged Arrows will not work, because you're spending Energy Shield, not Mana. You will need to use Ballista Totems with Focused Ballista Support, which is a bit annoying.

-Will Crafted +1 to Socketed AoE Skill Gems, (9-10%) Increased Area of Effect Prefixes on Helm and Gloves work?
Absolutely. Going for the +2 to Socketed AoE Skill Gems setups is an endgame optimization, and not required for the build to function effectively.