This build is the part of an optimised team comp to farm Yam, Sedna in Steel Path mode.

The only mandatory mod is [Despoil], thus [Nekros] is an easiest warframe in the comp to build for other functions, e.g. buff. We're using Roar for this simply because the most effective buff Warcry from [Valkyr] would slow enemies down out of our Larva range, meaning overall mission pace would be slower despite our comp having higher kill speed.

Warframe build

[Steel Charge] aura and [Coaction Drift] to increase our damage even more and because there are no auras that will be more usefull.

1. [Vitality] and [Rolling Guard] to help you survive random shots before enemies were caught into Strangledome.
2. [Stretch] in case you somehow managed to die, so you can instantly desecrate enemies' corpses after death.
3. [Umbral Intensify], [Blind Rage], [Transient Fortitude] are chosen as the most impactful mods in terms of Ability Strength.
4. [Primed Continuity] to balance out [Transient Fortitude] Ability Duration penalty.

Arcane Energize and Arcane Guardiаn to help you with sustain.

Operator build

Vazarin Focus School, so you can defend your allies with Protective Dash. Another option is Void Chrysalis in Unairu Focus School, but it takes much more operator energy and gives only 80% damage resistance compared to full damage immunity from Protective Dash.

Magus Cloud to easy use of Protective Dash. Magus Anomaly to help your second [Nekros] in case enemies got stucked on stairs.

Notes

1. [Adaptation] isn't a good idea because you usually either get one shotted because of Gorth [Ogris] or die because of fire patches on the ground after Zura shots. The only consistent way to stay alive is having a member with Vazarin's Protective Dash. Usually this member is you, 'cause after you used Roar and Desecrate, you can stay in operator mode as long as you want.
   However, if your party isn't familiar with strategy, feel free to swap [Rolling Guard] for [Adaptation].
2. Despite this and other builds from the comp are designed for melee weapons, feel free to use any Slash weapon you have a good build on (e.g. [Kuva Kohm]), because Ammo and loot drop tables are different. If you go this way, you can elevate it even further by bringing basically any weapon, but make sure you have equipped [Ripkas] with its mod [Amalgam Ripkas True Steel] which makes game to account every hit of our weapons as if it was dealt primarily with Slash Damage type.
3. Other Helminth options might be Warcry or Eclipse.
4. Arcane Guardiаn might be replaced with Arcane Aegis or Arcane Barrier.
5. Do not use Magus Lockdown because [Nidus]' Larva cannot pull enemies under its effect.