Of the weapons released with Sisters of Parvos, the [Tenet Flux Rifle] struck me with interest on its release due to its complete overhaul in functionality compared to the original Flux Rifle. From what became of a pretty mediocre beam weapon with high kill times compared to many of its held-trigger counterparts, the Flux was downplayed. No more.
The above build is built from hours of stress testing the weapon against countless enemies of varying difficulties in the ranges of Level 170+.
Recommenedations:
Regarding Progenitor frames, I would highly recommend a Toxin Progenitor, or a Heat Progenitor. Both elements assist this weapon's killing potential. Toxin can be combined with [Rime Rounds] (Viral) for general gameplay use, and Heat can be completely left on its own to help shred armor and fleshy targets alike.
If you choose Heat, feel free to replace your 60/60 elemental mod with [Heavy Caliber], [Vigilante Armaments], or [Hellfire]. (Will cost additional forma, though this is a Tenet weapon, so five forma is generally recommended anyhow.)
Also, if you find yourself without [Galvanized Chamber], replacing it with [Split Chamber] will get the job done. [Galvanized Aptitude], though important, can be replaced with [Heavy Caliber] if you are without it. Just rotate [Hunter Munitions] to the last slot and [Heavy Caliber] to that Forma slot instead.
For the sake of your eyes, I've included a Dark Mode variant of the Progenitor sheet for you to figure out what frames apply what elements in a Lich scenario.
Pros:
Guaranteed Status Procs
With the inclusion of [Flux Overdrive] on this build, the effective status of the Tenet Flux crosses 100%, making this one of the hands down best weapons for status procs on opponents, and opens the door for use of the new [Galvanized Aptitude] Mod, which functions very similarly to Condition Overload for melee weapons, making the kill times absolutely monumental.
Decent Base Critical + Multiplier
The fact that this weapon is great in both status AND Critical makes it excellent for the likes of Hunter Munitions, which absolutely trivializes enemy health pools when combined with Galvanized Aptitude.
Multishot
With the inclusion of a Multishot mod such as Galvanized or [Split Chamber], this more than excels the weapon's relatively low base damage into something far more modular. Balancing, of course.
Cons:
Status Reliant
Versus enemies such as Sentient Conculysts and Battalysts, this weapons suffers tremendously with damage output since they do not receive status procs from Slash. Bare this in mind for Steel Path when tackling Lua and certain Neptune nodes, that you will need a Melee (Paracesis) or otherwise a secondary or ability to be able to remove them from the fight.
Near-Necessary Exilus
Though it hasn't been talked about until now, [Vigilante Supplies] (or [Rifle Ammo Mutation]) is essentially required. Though nowhere near as ammo hungry as the [Tenet Tetra], this weapon has a Fire Rate of 15.00, and even without the help of Haste Motes or otherwise will chew through its 1200 ammo supply quite quickly. If you do not want to worry about the Exilus slot, then a companion with ammunition-assistance mods such as Carrier may be required.
Base Damage
Being that this weapon is the physical manifestation of a bullet hose, it suffers from a low base damage, which looks bad on paper and gives it quite a bit of work to perform with other weapons of its tier. Of course, base numbers aren't everything and builds like this and similar more than make up for it in raw killing potential.