UPDATE: This build has gone through a lot of testing and iteration and changed in two significant ways since the initial posting. The guide has been changed to [Reflect] these changes. Yes, it is costly at a combined three Umbra Forma, but the [Talons] build is much more freely customized than the base [Valkyr] build, which is where the resources are most importantly dedicated.

[Valkyr Prime Talons] Build (ALSO UPDATED): Here

Archon Shards: 5 Violet Shards for Critical Damage (Tauforged when possible)
Primary Weapon: Player preference with Primary Dexterity.
Secondary Weapon: [Vome Invocation] [Grimoire] with Secondary Dexterity. The rest of the build is player preference.
Normal Melee Weapon: Player preference, although [Dual Ichor] Incarnon is always going to be the strongest choice.
Focus School: Madurai for Power Transfer and Sling Strength.

Accompanying Mods: [Power Drain] Parazon mod. Fishing for Mercy Kills on Eximus enemies is very easy and grants +50% Ability Strength for Warcry and Hysteria refresh casts.

Prior to the launch of the Valkyr rework, there were so many people having an obnoxious knee-jerk negative reaction to Valkyr's total invincibility being removed. This thought process was based entirely on zero-creativity conventions as the release of the rework has proven just how insanely powerful [Valkyr] is.

The Highest Damage Reduction Ever
At max ability strength, this build allows for a 582% snapshot Warcry cast, resulting in +301% Attack Speed and a total of 5810 Armor after Warcry. [Hysteria] triples the bonus, resulting in an enormous 11520 armor, which gives a staggering 97.46% Damage Reduction on Health. Against 99% of enemies, which use multi-hit weapons, the 582 health heal from snapshot [Hysteria] hits means [Valkyr] has no problem staying at max health for a very long time. Normally, [Adaptation] would be an obvious choice, but the problem with [Adaptation] is that as enemy levels climb, it inevitably becomes dead in slot. Enemy damage eventually is able to bypass full buildup which, even though uncommon, renders [Adaptation] useless. As a result, [Hunter Adrenaline] is chosen to pair with Nourish for consistent and continuous energy stability. Lastly, thanks to [Valkyr]'s new passive, even if enormous damage were to surpass the damage reduction, [Valkyr] does not die, her abilities are not interrupted, and she is able to almost immediately rebuild her [Rage] meter during the 5 seconds of invincibility with an Attack Speed of 6.3.

Everything Must Die
The 300% additive Melee Damage from her [Rage] Meter is an enormous boon because it means the [Talons] are clearly built for Melee Influence. Routine Paralysis and Nourish casts grant an average +212% Viral from Nourish (without [Power Drain] or [Grimoire] since neither of them are intended for Nourish cast) and huge damage vulnerability resulting in tens of millions of damage. All hits are tier 2 red crits, giving a 57.5x crit multiplier on every attack before increased damage from Paralysis and/or Viral. There is no enemy level at which [Valkyr] cannot effortlessly destroy any enemy in the game.

Ability Breakdown
Nourish: In addition to its previously stated +212% Viral damage and free Viral procs for 2x damage vulnerability, Nourish grants a sky high multiplier to energy orbs and, most importantly, [Hunter Adrenaline], ensuring that [Valkyr] will always remain at her absurd 1225 max energy from Warcry for as many Paralysis casts as necessary.

Warcry: Explained above. No need to repeat. [Eternal War] is [Eternal War] and has always been [Eternal War] since [Eternal War].

Paralysis: While the slow is capped at 75%, the gigantic 246% multiplicative damage vulnerability is not. Neither is the 491% it can actually give with Viral added to the equation.

[Hysteria]: There was an uproar about the healing being changed from a percentage of health to a flat amount. However, at 601 health per hit, the difference is marginal and any hit that does not one-shot her is immediately irrelevant when whatever hit her and all their friends are already dead and her 2100 health remains fully restored.

Companion
Finally, [Wyrm Prime] is chosen for its incredible defensive capabilities to massively [Negate] enemy threats. With a [Shivering Contagion] [Verglas Prime] and multiple [Duplex Bond] clones created by Paralysis and Nourish casts, crowds of frozen enemies, paralyzed enemies, and enemies sent flying by [Crowd Dispersion] means there are very few left to threaten [Valkyr].

The [Valkyr] rework has presented an incredible opportunity. [Enraged] is off the table. [Prolonged Paralysis] is a thing of the past. The Damage Reduction she can create is higher than anything the game has ever seen or was ever thought possible. She is precisely what has always been impossible: A true end game level cap health tank. This should be celebrated, not derided. If you're looking for actual build variety and a new way for this warframe to finally be fun again at even the highest possible levels, then this build is absolutely for you.

Alternat Companion
If you get your hands on a Critical Chance Riven for a [Verglas Prime], then a [Diriga] with the [Verglas] for consistent Heat and Electric crowd control along with status spread becomes your new best friend.