INTRODUCTION

Felarx is a full-auto projectile shotgun that feels like an automatic Exergis, that transforms into semi-automatic dual pistols. We will mostly be using the Primary Shotgun mode due to the higher base damage, innate multishot and better feel of full-auto trigger, but the build would also work well for the incarnon mode. The non-incarnon mode also has infinite body/enemy punchthrough.

Due to the Devastating Attrition perk giving 2000% damage multiplier on 50% of non-crits, we build Felarx for a raw damage non-crit build and take advantage of shotgun's access to TWO Primed elemental mods ([Primed Charged Shell] and [Primed Chilling Grasp]). You can either build for raw Viral + Electric or raw Corrosive + Cold. Corrosive + Cold is the best damage type for general use against armored and shielded enemies, as Corrosive ignores 75% of ferrite armor and has a +75% bonus against ferrite armor, which is possesed by many heavy units (including Acolytes, Demolysts and Liches/Sisters) while Cold has a +25% bonus against shields and alloy armor. This will probably allow you to one-shot Liches. Viral + Electric may be a niche choice for unarmored and grouped enemies, particularly when shot into Magnetize Bubble or [Zephyr] Tornado. Viral Heat is less effective due to the overall lower effective status chances (low base split among multishot) and lack of primed heat mod, but is an alternative.

An alternative playstyle that I prefer, that may not be for everyone, is to use a secondary or melee primer and constantly swap to reload (only 1.7s for full 13 clip reload with Evolved Autoreloader perk) and prime for mega boosting the multiplicative [Galvanized Savvy].

EVOLUTION CHOICES

1. Incarnon Form : Land headshots to build up charge.
2. Frictionless Flight : +50% Projectile Flight Speed OR Kinetic Baffle -50% recoil (combines with Deadhead to be 100% recoil reduction). This is mostly personal preference, if you are okay with the minor recoil it has.
3. Evolved Autoreloader: allows you to bypass the insane reload time, allowing full reload in 2s of swapping weapons (or just 1.7s with two Synth mods). Combine with a Primer or use a melee to quickly switch between weapons. Mounting Momentum is an alternative that gives +10% fire rate for each shell reloaded. If you reload 13 shells from empty, you can get up to +130% fire rate for the next 13 bullets, but the total reload is still about 3s long. If you want this, drop shotgun spazz for primed tactical pump. The non-incarnon form actually has infinite body punchthrough, making the dual mode chamber perk useless.
4. Wracking Wrath: +20% status chance, -10% crit chance. Improves chances of Devastating Attrition proc
5. Devastating Attrition: 50% chance to deal 2000% damage on non-crits. Presumable similar to Devouring Attrition, being multiplicative to base dmg sources.

MOD CHOICES

• Galvanized Hell : +230% multishot at max stacks,
• Galvaznied Savvy: +80% dmg per status, so potentially +400% dmg after 5 statuses, or even more with priming. Apparently multiplicative with +dmg sources like Primed Point Blank and Primary Deadhead
• Primed Ammo Stock : turns magazine size from 6 to 13. If you reload from empty, you can gain +130% fire rate from full clip.
• [Primed Tactical Pump] : cuts long reload speeds. Use [Shotgun Barrage] instead if you prefer to use Evolved Autoreloader perk (stack with Synth set for about 60% reload per second of holster, or basically full reload in 1.7s upon switching to a primer or melee).
• [Primed Cleanse Grineer] : Multiplicative 55% to other +dmg sources. Flexible for Primed Point Blank (only slightly worse overall DPS, best used for Acolytes/Thrax/Factionless or if you don't like swapping faction mods).
• Primed Charged Shell/Contagious Spread/[Primed Chilling Grasp] : maximum elemental damage for raw corrosove + cold. Switch order to make viral + electric if desired, or add Incendiary Coat or Blaze over Primed Chilling Grasp to make Corrosive/Heat. Add [Incendiary Coat] over [Primed Charged Shell] and reorder mods to make viral heat. [Primed Chilling Grasp] is flexible for Chilling Reload. Contagious Spread is alternative to Toxic Barrage (needs more forma for tiny damage boost). Can use non-primed versions or 60/60 versions of any elementals if you don't own them or can't fit them.

Arcane
Flexible choice

• Primary Deadhead : +360% dmg after just 3 headshot kills which multiplies with Galv Savvy, recoil bonus and extra 30% headshot multiplier.
• Primary Merciless : +360% dmg but needs 12 kills and drops stacks quickly, ammo maximum and reload bonus go very well with [Felarx]

Other factions
For Corpus: Swap faction mod to corpus and [Contagious Spread] for [Incendiary Coat] to make RADIATION + COLD. This is because cold has a 50% bonus against corpus shields and Radiation has 75% bonus damage against alloy armor possessed by most corpus robots, which are the tougher corpus enemies). This also allows you to maximise [Xata]'s whisper if you choose to use it.
For Index: Swap faction mode to corpus, [Contagious Spread] for [Incendiary Coat] or [Blaze] and make sure final elements are RADIATION + COLD (radiation and cold both have bonuses against Alloy armor possesed by every Index enemy and cold has a +50% bonus against Shields). This setup can also be used for corpus.
For acolyte/thrax: Swap cleanse mod for [Primed Point Blank]
For infested(particularly Deimos): Can consider [Blaze] over Primed Chilling Grasp to make Corrosive Heat.
For Archon: Swap faction mod for primed point blank and Contagious spread for incendiary coat/[Blaze] to form RADIATION + COLD (Archon is alloy armor).

SYNERGIES

Devastating Attrition functions like Devouring Attrition and double dips on [Xata]'s whisper so the void damage instance of [Xata]'s Whisper becomes damage x 21 x 21 x 25% x strength.

Magnetize and [Xata]'s bubbles also synergize with the infinite punchthrough property

Demonstration of using a primer, autoreloader and synergy with [Xata]

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