This is a build specifically to be used with [Saryn]'s Toxic Lash + Full strip with spores. This is because by itself, Acid Shells isn't very good in Steel Path, as it currently ignores SP modifiers and scales off the max health of a non-SP enemy (i.e. it is 2.5x weaker than advertised in SP). Also while [Acid Shells] scales with HP, it deals corrosive + blast damage in AOE which require full armor strip to be effective. When used with [Saryn] however, [Acid Shells] is capable of inducing a chain reaction that can spread across an entire map. When an enemy is killed with Toxic Lash active, [Acid Shells] will deal 450 corrosive dmg + 45% HP blast dmg in a 15m radius, and each enemy hit will have a toxin DoT created that scales off the [Acid Shells] damage. If this new enemy hit subsequently dies from the Tox DoT, it will create another [Acid Shells] explosion centered on this new enemy. As long as enemies stand within 15m of each other, this chain reaction can spread across a map.

PROGENITOR

The Progenitor type is completely optional since it DOESN'T affect Acid Shells or Toxic Lash. You could do Toxin which is the most flexible element (allows you to run Viral/Corrosive/Toxin on a non-Acid Shell build), Electric (allows easy swapping between Corrosive, Radiation, Viral Electric) or even Magnetic (gives free extra element for [Galvanized Savvy] and doesn't mess with elemental combinations).

CALCULATIONS

After testing, the Progenitor Bonus, Critical Multiplier and Base Damage all do NOT affect the Toxin DoT of Toxic Lash when triggered by [Acid Shells] AOE explosion. The formula for Toxic Lash DoT scaling from [Acid Shells] AOE is :

(450 + 45% HP) x (1+toxin mods) x ( 1+ toxin mods + other elemental mods) x (1+faction mods)^3 x (1+status damage)

As you can see faction mods TRIPLE DIP, toxin mods DOUBLE DIP while elemental mods and status damage mods single dip on the Tox Lash DoT.
Note the HP is for base starchart values, ignoring the steel path 2.5 modifier.

MOD BREAKDOWN

Galv Savvy - helps get the initial kill to start chain reaction, but does NOT affect [Acid Shells] or Acid Shell Tox Lash DoT. If you run primary merciless, this slot should be replaced with Elementalist or Shotgun Barrage.

Primed Cleanse Grineer/Corrupted/Corpus/Murmur - faction mods TRIPLE DIP on toxic lash toxin procs by boosting your weapon damage, boosting toxic lash damage on hit (which scales off weapon damage) and boosting toxic DoT (which sclaes off the first two).

Toxic Barrage and Contagious Spread - Toxin mods DOUBLE DIP on toxic lash procs by multiplying the toxic lash damage and toxic DoTs

Primed Chilling Grasp and Primed Charged Shell - elemental mods boost weapon damage which increases both the initial toxic lash damage and the resulting DoT

Shotgun Elementalist - boosts toxic lash status dmg by another 1.9x

Arcane:
Primary Merciless is needed for base damage if not running Galv Savvy
Primary Blight is a great option when running [Saryn] since Toxic Lash triggers primary blight meaning you don't need any ramp up if using merciless.

FLEXIBLE OPTIONS

If you are NOT using [Saryn] with Toxic Lash, you can drop [Toxic Barrage] for [Shotgun Barrage] or [Primed Point Blank]. [Primed Charged Shell] is also flexible if you are not using grouping or armor strip.

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