Level 96 Crit Cyclone of Tumult Slayer^3.25

Notes

FAQ 

Why not Champion for 3.26 as a league starter?

I believe Champion is somewhat misleading as a league starter recommendation, while Slayer offers significantly higher damage output. 
To make fortification builds work effectively, you'll need costly unique items from trading, which won't be readily available or affordable early in the league. 
Additionally, you'll need to craft a chest piece with stun immunity because Unwavering Stance conflicts with Perseverance. 
In my opinion, suggesting Champion outperforms Slayer for league start (especially in the first few days) isn't accurate. 
A better approach would be starting with Slayer, then transitioning to Champion once you've acquired the high-value items needed to maximize its damage and defensive potential. 
Just expect to invest a substantial amount of currency.

Why not Axes or Maces or Swords, why Staves?

I'm not using Axes or Maces or Swords because I'm running Shockwave Support, which only works with Maces, Sceptres, and Staves. 
Out of those three weapon types, Staves are the clear winner since they allow me to scale Block for additional tankiness. 

Is the Stampede necessary? I'd rather move faster.

The Stampede is necessary because Cyclone of Tumult significantly reduces our movement speed, and these boots are the only effective way to counter that penalty.
If you prefer faster movement, you can certainly use regular Cyclone instead, but you'll sacrifice both damage and area of effect coverage.

When to swap to Crit/What do I need?

When you acquire a staff with solid physical DPS, it's time to transition into a critical strike build. 
First, ensure you're hit-capped by investing in the Eagle Eye passive cluster and taking the Mastery that provides +500 Accuracy Rating (with -2 per level). 
Additionally, run the Precision aura to further boost your accuracy and crit chance. 
For your critical strike scaling, spec into Smashing Strikes to generate endurance charges from crits while increasing your crit chance. 
Also invest in Disemboweling and take its Mastery for +25% Critical Strike Multiplier against Unique Enemies.

What about the new Unique Starcaller?

Starcaller's physical DPS is too low for our purposes. It appears to be better suited for a Cast on Crit build.
New Wave of Convinction looks interesting for this...more to come.

LEVELING

In Act 1 use Spectral Throw with a physical 2H Axe until you get Sunder before Merveil. 
Use Sunder with a physical 2H Axe until Act 3 when we swap to Cyclone and General's Cry. Make sure you have a good physical DPS staff when you swap.
To craft a good physical DPS axe or staff, sell a weapon + blacksmith's whetstone + magic or rare rustic sash to a vendor - this gives you back the weapon with increased physical damage.
Then bench craft on attack speed.

See the provided loadouts for gem suggestions and tree pathing.

The leveling loadouts include attribute notables like "Hard Knocks" and "Proficiency" to help meet stat requirements early on, particularly intelligence for staves. 
These are temporary solutions for attribute pressure - if you're already meeting your gear's attribute requirements, you can skip these notables entirely and invest those points elsewhere.

REGEX

Vendors in Act 1/2: we mostly are looking for a G/G/R for Spectral Throw, a R/R/R for Sunder, a R/G for Leap Slam, as well as movement speed boots: 
r-r-r|g-g-r|g-r-g|r-g-g|g-r|r-g|nne|rint

Map modifiers to avoid:
om$ ur$ gen uct "s rec" rses non

SSF ATLAS TREES (NOTE SUBJECT TO CHANGE WITH 3.26, WILL UPDATE IF NECESSARY)

TREE 1 - Expedition/Harvest/Jun for crafting gear (I don't grab Unwavering Vision, I like scarabs :P)

I typically use my first tree to farm league mechanics that will help me craft gear and get easy currency drops.

TREE 1 - 30 Points
Allocate points for more map drop chance, as well as higher map tier and Kirac missions. Take "Shaping the Skies" and "Shaping the Mountains" before "Shaping the World".
https://poeplanner.com/a/aMK

TREE 1 - 43 Points
Grab "Obseesed with Vengence" on the way to "Hunt for Answers" to spawn Jun and Expedition. Then grab "Call of the Grove" to spawn Harvest.
https://poeplanner.com/a/axo

TREE 1 - 60 Points
Next we go for "Ancient Writings" and "Distinguished Demolitionist" for better Expedition QoL. Then go for "Bumper Crop" and "Bountiful Harvest" for more Harvest juice and XP.
NOTE: I don't take "Extreme Archaeology" as it can be very rippy on a league start when you're still fixing resists/physical damage redutction/etc. If you want, go for it.
https://poeplanner.com/a/ax-

TREE 1 - 77 Points
Now move up to the far right to grab the Expedition wheel for "Rather Not", "A Noble Quest", and "Scratchin' Up the Ground". Then grab "Doubling Season" for more Harvest juice.
I like Tujen for bubblegum currency and Rog for crafting.
https://poeplanner.com/a/axI

TREE 1 - 97 Points
Finally, we head to the middle for "Buried Knowledge" and "Heart of the Grove" for more Expedition logbooks and better Harvest crops.
https://poeplanner.com/a/ax2

After this, you can spend points on TREE 1 however you prefer. I like to add Harbys and Shrines since they are close by, for example:
https://poeplanner.com/a/axb

TREE 2 - Boss map generation/Scarabs/Shrines (This helps us get our last 2 voidstones and is also good)

The concept here is we run maps that are witnessed by Maven. By clearing the whole map and then going to the boss, Maven will spawn additional bosses.
This gets us more influenced maps. You can favor Silo maps and run them, when you get to boss room kill all the bosses and leave before killing Silo boss.
By doing this, you can run Silo over and over and get Maven to still witness the map.
Otherwise, rotate between different maps to get Maven to witness.

TREE 2 - 68 Points
Grab "Shaping the Skies" and "Shaping the Mountains" before "Shaping the World", then head all the way north for "Remnants of the Past" and "Destructive Play".
This gets influenced map drops on boss kills so we can farm frags for Elder and Shaper. Grab the Shrine nodes for QoL.
https://poeplanner.com/a/aqL

TREE 2 - 106 Points
Pick up "Vivid Memories" and "Conquered Conquerors" to get more boss maps for Cortex and Sirus.
https://poeplanner.com/a/axf

TREE 2 - 132 Points
Grab remaining scarab nodes and allocate anything else on top of this you'd like:
https://poeplanner.com/a/axV

TREE 3 - Any league mechanic you want, I've provided a few examples.

This is a blight farm tree. Use this to get blight maps. Run blight maps and blight-ravaged maps to farm The Stampede. Also for farming Essences.
Use one Opalescent and one Silver oil to annoint "Your Chilling Towers freeze enemies for 0.2 seconds while they are affected by chilling beams" on first ring.
Use one Indigo and one Violet oil to annoint "Your Meteor Towers create Burning Ground for 3 seconds on Hit" on second ring.
When doing blight and blight-ravaged maps, build Chill towers at chokepoints on lanes to freeze mobs. Build a Meteor tower behind it to kill them. Buff both with Empower towers.
Invest 3x into the Chill and Empower towers, max out the Flame towers to convert them into Meteor towers. Profit.

TREE 3 - 132 Points
https://poeplanner.com/a/aqQ

TENTATIVE MERC IDEAS 

Possibly using a link skill with mercenary and going for the link mastery that matches our movement speed to that of a linked ally (to negate Tumult's downside).
Running determination for more PDR.