Preface

Want your squadmates to ask you how the heck they're doing crazy numbers? Wish to see your companion do funny numbers while you just kind of chill? Would you like to bring a weapon that isn't as juiced up into steel path and make it eat your enemies alive anyhow? Welcome to my favorite Herald of Death, [Banshee]. One of the most underrated but most fun frames I've encountered as a more recent Tenno. So, if you don't know much about her, strap in! This build aims to show you my favorite way of running Banshee with teammates while also providing you information to tailor her to your own playstyle.

This is a support/buffer endgame build of [Banshee] that utilises her most damage amping ability in her arsenal, Sonar, alongside it's even more powerful augment, [Resonance], to give you, your companion, and all of your allies the incredible ability to slice through anything without damage attenuation like butter. This is due to its multiplicative nature, making Sonar one of the best damage buffing abilities in the game. At base strength, a weakspot does x5 damage. Two weakspots overlapping turns that into x25. And some specific enemies, specifically non-humanoid enemies such as the Murmur, have the capacity to continue increasing this damage exponentially due to the way weakspots generate on Murmur vs humanoid enemies; sometimes it may stack x3 or x4 times on the same spot. I believe this is possible on Techrot as well (despite being "humanoid"); however more testing may be needed on my part to confirm that.

Sonic Boom is decent crowd control that ragdolls enemies away from you, good for getting enemies that like being in your face, like Techrot and Infested, from getting too close. It will also armor strip with the augment Sonic Fracture and a bit of ability strength; however this is typically unnecessary with the ridiculous damage and/or CC you can attain with Sonar and whatever you subsume over her 4th. Sonar's ridiculous range means that you don't need to spec too much into ability range, especially if you decide to subsume Gloom over her fourth. Silence, her subsumable ability, is incredibly good at shutting down anything remotely dangerous that doesn't get shredded immediately, i.e. acolytes and eximus units. Soundquake is a relic of a bygone era, and no longer has its incredible nuking capability it had years ago, so this is almost always her subsume slot unless you decide to do low-level shenanigans with [Resonating Quake].

Gameplay

Cast Silence and Roar (or whatever is subsumed here). If you have additional sources of conditional ability strength (i.e. Madurai / Molt Vigor / Pax Bolt), activate those first.
Spam Sonar a few times as energy allows for it, trying to proc the chance for her weakspots to overlap. Usually I like it when the enemies are all shiny before I fire upon them.
(Optional: Cast Sonic Boom to ragdoll enemies away from you, handy for getting enemies off you or a defense target.)
Recast Silence and Roar as needed.

Flexible Slots

Aura:
Brief Respite for shield gating, can alternatively use 3 augur mods on your secondary/warframe for the same effect.
[Growing Power] for increased ability strength on status.
[Corrosive Projection] for damage increase, nice with viral stacks and no other external armor strip.

Exilus:
PSF for knockdown resist, [Handspring] is a very close second for very fast knockdown recovery. No PSF saves you a forma.
[Vigilante Pursuit] (pair this with a primary that has [Vigilante Supplies] and a sentinel weapon with [Vigilante Armaments] for a total of 15% from its set bonus.)
Drift Mods
[Preparation]

[Blind Rage]:
Negative efficiency isn't strictly necessary for shield gating with [Brief Respite] and [Catalyzing Shields] since Sonic Boom will fill half of your shield capacity and a cast of Sonar will bring it to full, giving you your 1.33s i-frame window to survive. Swap this according to your playstyle, i.e. Rolling Guard for an extra 3 seconds of i-frames, [Equilibrium] if not running [Equilibrium] shards or increased energy gain (amber) shards, [Sonic Fracture] for armor strip on your 1, R5 [Blind Rage] if you want the extra strength but 45% energy efficiency is too burdensome.

[Archon Stretch]:
Slight passive energy [Regen] but not strictly necessary as its not contributing a huge amount to our energy economy with how often we are casting 2. Can replace with normal Stretch.

Arcanes

Power Strength arcane, i.e. Molt Augmented / Molt [Vigor].
Energize for energy recovery, expensive.
Aegis for survivability.

Since [Banshee] is a weapon platforms frame, we're welcome to run weapon buffing arcanes as well on her, depending on your playstyle.
[Rage] for +primary damage on headshot.
Precision for +secondary damage on headshot.
Fury for +melee damage on crit.
Arachne for +primary/secondary damage on wall latch.

Subsumes

Her 4th is her default subsume slot.
Roar for buffing your DoTs and damage. Your companion and teammates will very much enjoy this; this build reaches 129% roar, so nothing to scoff at.
Eclipse for buffing weapons, requires augment to share with squadmates.
Wrathful Advance for a melee platform [Banshee].
Breach Surge to proc potentially really funny sparks, try throwing on Worthy Comradery to boost your spark damage.
Gloom for ultra-slowing enemies, including acolytes and liches. I would go check out ninjase's build here, they have a detailed guide on the playstyle and it's pretty fun even if Gloomshee is kind of a go-to pick. It's still really fun! Requires 272% str for gloom slow cap.
Nourish... duh? Amped up energy [Regen] on a fairly energy hungry build.
Evade for invisibility; opens up options like Arcane Crepuscular and [Spectral Serration]. Her weakspots are not considered weakpoints, these are two distinct entities and DE has said they're not planning to make any specific interactions between Banshee's weakspots and enemy weakpoints. However, with how much you may cast Sonar and it's self-propogation with [Resonance], you're bound to land a weakspot on the head anyway.
Resonator for DJ [Banshee], helps with survivability and thematically fits with her Soprano skin. Style is everything, after all. :3
...and really, this spot is so flexible you can really just throw whatever you want on here to fit your needs, just adjust your mods to meet your needs. You'll always have access to [Precision Intensify] if your subsumed ability requires strength, otherwise that could just as easily be a flexible slot.
Ophanim Eyes for armor strip/slow, also very thematic with banshees in folklore/mythology!

Archon Shards

2 Amber Cast Speed Shards, required to spam Sonar and cast Silence/Roar super quick.
3 (Flexible) Slots, I personally run 1 Tau Amber Parkour Speed and 2 Tau Violet [Equilibrium] Shards for about half of the equilibrium effect.
Alternatively, you can run 3 Crimson Strength Shards to drop Molt Augmented / Molt [Vigor] for something else.

Companions

[Dethcube] + Energy Converter
[Nautilus] + [Cordon]
[Helios] + [Vicious Bond]

Pair them with Blast + Tox for an aoe effect on 10 stacks and death (both of which should happen quick), Viral Heat for highest dps single target damage. Viral Elec Cold [Artax] or Viral Heat [Angstrum] are viable primer alternatives.
(potentially will make builds to link here eventually, but there are quite a few up to date setups for these so not gonna bother atm.)

Conclusion

Your... your world is your oyster! I'd say this is a fairly cookie cutter setup for [Banshee], but there's beauty in the simplicity of older frames that can do incredibly well in today's meta. Powercreep has crept up so hard that well, throw something on and see if it works because it just might! She is honestly incredibly flexible with most of her abilities ranging from useful to what the heck, this shreds! Her 4 is definitely in need of some love, but having the option to run whatever over it and have access to [Precision Intensify] is honestly something I don't [Hate]. This build, and just [Banshee] as a whole, will take you pretty far into content if you let her, so let's show her some love! And maybe DE will get to as well for the first time in awhile. :3