Alternate Mods: [Handspring] vs. Primed Sure Footed; staying knocked down while not invincible is a death sentence.
Archon Shards: Two Violet Shards (20/20 or 30/30 health and [Energy Conversion] each), three Crimson Shards (Ability Strength)

Primary Weapon: [Tenet Arca Plasmor] is preferable; overall build is malleable.
Secondary Weapon: [Xata Invocation] [Grimoire]; overall build is malleable. This is used to guarantee an initial Grave Spirit cast at the beginning of the mission.
Melee Weapon: [Coda Pathocyst] build: Click
Focus School: Madurai for Chained Sling and Sling Strength.

[Dagath] has naturally perfect Shield Gate capability with a [Catalyzing Shields] modded 50 base shield to be restored via [Brief Respite] alone with any ability cast. [Augur Message] allows further overshield accumulation during her Spectral state.

[Spectral Spirit]
[Dagath]'s augment gives her the capability to be frequently invincible and, during that invincibility, spread Doom to any enemy hit by her weapons and, most importantly, any damaging ability. At max Ability Strength from Molt Augmented and Sling Strength, Doomed enemies take an enormous +388% weapon Critical Damage. However, [Dagath] does not have a means of increasing weapon Critical Chance and would normally rely on weapon mods to pick up the slack. While not invincible, the combined utility of Wyrd Scythe's 95% slow and Fire Blast's knockdown allows her to continuously shield gate and [Neutralize] threats to her shield. This gives her every opportunity to kill groups of enemies and decrease Grave Spirit's cooldown. The wealth of health orbs and energy orbs that she was not able to pick up in Spectral form supplement repeated casts and uninterrupted Shield Gate.

Fire Blast
Fire Blast perfectly covers every hole in [Dagath]'s game and accomplishes more than was ever previously possible. With [Spectral Spirit], every enemy hit by Fire Blast's enormous 36.3m radius AoE becomes Doomed and loses 75% armor from a single cast. Enemies without Overguard are knocked down and suffer a Heat proc. However, because [Dagath] never faces an Energy drought, both as a result of all enemies dropping health orbs on death during her Spectral State (with the two Violet Archon Shards) and her passive buffing energy orbs on 35% of pickups, she is able to repeatedly recast this ability. Enter Arcane Hot Shot. Through multiple Fire Blast casts, [Dagath] is able to quickly build +300% weapon Critical Chance and fully strip enemy armor alongside Wyrd Scythe's forced Viral procs on the very same enemies. [Coda Pathocyst], with Melee Influence, is then able to obliterate entire squadrons of enemies, either creating huge pools of health orbs for infinite energy (during Spectral state) or eliminate the Grave Spirit cooldown (outside of Spectral state).

With all of these elements combined, Dagath becomes an unkillable, room-clearing monster with a very active, engaging playstyle. Following the Techrot Encore update, she has easily become the most underrated Warframe in the entire game and remains criminally underutilized. If you're looking for a different Warframe to play without losing your power capabilities, she is now definitively one of the best options available.