Solo Sustain - The Eternal
The goal of this build
The build is heavily focused on self-sustain. You will easily be able to [Recover] your health and energy, while delivering high damage across a small area or against priority targets.
[Umbral Vitality] and [Umbral Fiber]: These mods boost the effective health of [Valkyr], further being boosted by her Warcry. These stats are needed to sustain hits outside of Hysteria to [Recover] the energy cost of her skills and to be able to sustain all of her abilities.
[Hunter Adrenaline] and [Primed Flow]: This mod is important because it allows us to quickly switch to our primary weapon while Hysteria stays active, which disables the immunity provided by it. Any damage to our health we now take will partly be converted back into energy for uptime of Hysteria. [Primed Flow] further boosts the amount of energy we can store and allows us to run Hysteria for extended periods of time.
[Eternal War]: The usage of this augment for Warcry allows us to cast the ability once, but keep it up due to additional time being added on kills while the buff is active. It removes the energy cost of re-casting the ability and allows us to stack the buff up further, or keep it active for longer periods of time without kills.
[Narrow Minded] and [Primed Continuity]: Since both Hysteria (passive energy consumption) and Warcry (duration of the initial cast and time added by the augment) work well with bonus duration and range isn't a needed factor for our goal, these two are the optimal options when it comes to lowering our overall energy consumption. The base cost of her abilities isn't high enough to justify spending mod slots on efficiency.
[Umbral Intensify]: Overall strength of her abilities, higher buff from Warcry and additional boost for [Umbral Vitality] and [Umbral Fiber].
How to use this build
Activate your WarCry at the start of the mission, in most cases it can easily be sustained to stay active for the duration of the mission. Hysteria allows for heavy damage against priority targets, but still allows you to quickly switch over to your weapon for additional sources of (ranged) damage. If your Hysterias energy consumption starts getting too high (percentage in the bottom right), switch over to your weapon - which ends the invincibility - and deactivate it to avoid suffering from the damage you would otherwise take. When needed [Recover] energy by easily tanking hits to your health, which will convert parts of it into energy. This can also be done by simply switching to your weapon, without canceling Hysteria, if your energy consumption is at lower levels still. The high amount of melee focused bonuses (WarCry, Steel Charge and Coaction Drift, or - again entirely optional - arcane enhancements like Arcane Avenger or Arcane [Fury]) also allow for heavy usage of your melee weapon with Hysteria being deactivated.
Build changes without umbra polarity
You can play this build just fine without using up a umbra forma by switching out Primed Flow for a rank 4/5 [Flow], while dropping the [Coaction Drift] mod from the Exilus slot. This slightly lowers your overall damage output and allows for less reserves when converting health to energy, but still allows you to survive content far beyond sortie levels just fine.