I decided to share my Build for [Nidus] here as the Top one on this site is outdated. Loads of Text here but please read if you realy want to understand why each mod is where it is.Note: This is the "Budget Build" if you have loads of Forma you can max out most Mods here without any issue.
- Aura: [Corrosive Projection], [Growing Power], Powerdonation, Swift Momentum, Steelcharge.
(I recommend using an Auraforma because any of these Auras benefit you solo or if you play in a Team)
Exilus: Primed Sure Footed, Sure Footed
(Spend less Time on the ground, more Time on Killing)
Main Mods: [Umbral Intensify], Fiber, [Vitality], [Adaptation], [Rage] or [Hunter Adrenaline],
(All Umbral Mods stack with each other, Nidus has no Shields and Benefits from all three Mods. Adaptation is usefull / doesnt have to be max rank even works on rank 0, Rage or Hunter Adrenaline to get Energy by taking Damage, Stretch for Range on his 1st 2nd and 3rd Ability)
Optional Mods: [Power Drift], [Augur Secrets], [Augur Reach], [Flow], [Shock Absorbers], [Carnis Carapace], [Gladiator Resolve], [Nidus] AUGMENT MODS *
(Note: These are not all the Mods you can use. You can put more Forma into him and use any Mod you want, these are just the ones that I personally use in certain Builds!)
Arcanes: Grace, [Guardian]
(Only use em if you own them they are not Mendatory but increase EHP and overall tankyness. As [Nidus] doesnt have Shields Grace and Guardian have a high Uptime and you passivly benefit from both Arcanes pretty often)
-If you run Steelcharge or Powerdonation you get more Modpoints which can be spent to optimize some Mods: Slot in Hunter Adrenalin instead of Rage, use a higherranking Adaptation Mod (I recommend to only upgrade it to rank 10).
-[Nidus] is not affected as much as other Warframes by negative efficiency as his 3rd and 4th Ability dont need Energy to cast. They both use his Stacks which are gathered by hitting enemys with his 1st Ability. Thats why you can swap out [Transient Fortitude] for Blindrage and get the Energy used by his 1st Ability refunded at a higher rate (more risk for casting but better refund)
-Swap out Augur Secrets for Power dirft if you dont have it (its more accesable for newer Players)
-Umbral Mods come from the Quest "The Sacrefice" (If you dont have them you can use the normal Versions they work just fine)
-Negative Duration from [Transient Fortitude] is not bad. It even cuts down the duration your Larvas stay active should you misscast it but it lached only onto one enemy. You still have 45sec on your 3rd and cast time is so fast you swap targets all the time anyways.
Use any Augment for Nidus except Abundant Mutation! -> The cooldown on his passiv can screw your survivability in higher SP endurance Runs or Arbitrations!
You dont need 300%+ Powerstrenght on him for solo or casual play. Most people want 300% to Buff other Frames with his 3rd Ability for example Chroma for his Vex armor.
Don't replace his 1st, 2nd and 3rd Ability with any Helminth Abilitys! All three have great Synergy and are meant to be played that way. (Note: You can swap out his 2nd if you have other Means to group up Enemys OP-Arcanes, [Khora] etc.) You CAN replace his 4th with any Helmith Ability and experiment. (Use Lifestrike or Healing return on your melee or OP-Arcanes / Vazarin to heal you)
Don't put mods on him that increase duration (Only if you need it for Helminth abilitys). His default or even lowered duration (by Transient Fortitude) is fine. Just recast his abilitys he is a Caster-Frame after all....
Final Words: My Version of [Nidus] has two Umbral Formas on him to fit maxed Mods into him. He is the best Tank ingame if you know how to maintain the Stacks and pair him with some Powerfull weapons. Thanks for reading this long description. Cheers :)