Level 85 Toxic Rain Totem Pathfinder^3.21

Notes

Poe Pathfinder is a great choice for players who enjoy an adaptable and versatile playstyle that can handle a variety of challenges. With their unique flask mechanics and diverse skillset, Pathfinders can be a formidable force on the battlefield. Toxic Rain Ballista Pathfinder is a highly versatile and powerful build that can deal massive damage while remaining tanky. 
Firstly, you'll want to focus on getting a good bow that has increased physical damage and attack speed. You'll also want to look for mods that add chaos damage over time, as Toxic Rain is primarily a chaos damage skill.

Skill tree
you'll want to work on your skill tree. The most important nodes to focus on are those that increase bow damage, life, and evasion. You'll also want to grab nodes that increase chaos damage, attack speed, and projectile damage.

Ascendancy
For your ascendancy, you'll want to choose the Pathfinder class. The Master Toxicist node is essential, as it greatly enhances your chaos damage output.
 Nature's Reprisal is another great node to pick up, as it can cause enemies affected by your Toxic Rain to explode, dealing even more chaos damage to nearby enemies.

Gear
When it comes to gear, you'll want to focus on items that increase your life, chaos damage, and attack speed. Look for items that have these mods, as well as increased physical damage and evasion.
 You'll also want to prioritize items that have resistance to elemental damage.

Flasks
In terms of flasks, your life flask is your most important one. Look for one with the "Bubbling" or "Seething" prefix, and a "Soul of Steel" suffix to help mitigate incoming damage.
 You'll also want a Quicksilver Flask to increase your movement speed, as well as a Jade and Granite Flask to increase your evasion and armor respectively.

Jewels
When it comes to jewels, look for ones that have mods that increase bow damage, chaos damage, and life. 
You'll also want to prioritize jewels that have the "Corrupted Blood cannot be inflicted on you" mod to help mitigate one of the most dangerous mechanics in the game.

In summary, a Toxic Rain Ballista Pathfinder build is all about stacking chaos damage, attack speed, and life. 
By focusing on these areas, you can create a build that can dish out massive damage while remaining tanky and survivable.
 Remember to refer to the tips mentioned earlier in this guide, and keep experimenting with different gear and skill tree combinations to find the perfect build for your playstyle.