The Galaxy NeedUs
Hello there,

Nidus Prime is one of those Warframes, in which I used up to two Umbra Formas. Why? Because in my opinion, he is almost perfect. There are really few such Warframe with such an excellent mechanic and such a wonderful synergy between skills.

Nidus can deal enormous damage, crowd control like no one business, strengthen himself and allies, heal.

He is an ideal choice for almost every kind of mission, almost, because on Spy he is the same level as the log. I do not say that he can not finish Spy Mission, but his skills are not useful there.

So I used two Umbra Formas to adapt him to universality as much... Thanks to this you have enough space for a lot of combinations, you can freely change the build depending on the demand for a mission.

Augments and Strain Set Mod:
Do you want to go for longer endurance? There is no problem, the above build should fit perfectly.

Do you intend to take a few short and quick missions, but you also want to use skills? No worries, choose yourself an interesting augment or Streamline instead of Umbral Fiber and go with the flow (you will not need more survivability).
I do not recommend Abundant Mutation tho, it is a double-edged sword... in long endurance runs it boost your damage, but only to some point... but also it can make you dead in a second. Nidus don't have shields, so he can be one-shot easily, and 30s cooldown is just horrible.

Do you want to play a bit, in an unconventional build? Give him Strain Consume and fill the room with maggots.
About Strain Mod Set, keep that in mind that the Set comprises 1 Warframe Mod, 2 [Helminth Charger] Mods, and 1 Melee Mod. The Strain Mods do not interact with Nidus's abilities or the maggots spawned by the [Pathocyst].

Aura! Any:
I suggest Aura Forma in an Aura slot to change them depending on the demand of the mission. Corrosive Projection is just one option, but I may suggest Auras like Enemy Radar, Energy Siphon, Growing Power, Mecha Empowered (for Mecha Set Mod), Rejuvenation, Shepherd, Shield Disruption, Stand United, Swift Momentum, Steel Charge.

Exilus! Primed Sure Footed:
I gave him Primed Sure Footed on Exilus, the reason is obvious, you will use AoE weapons, and you do not want Stagger. You are not always hooked up to the mob, Parasitic Link skill is mostly used when it starts to get really hot.

ENJOY!
THeMooN85