Okay, this is ACTUALLY my fully-updated what-I'm-using-now [Inaros] Build.

This is my current 'main'. He's pretty much invulnerable unless you go AFK to get a sandwich while in a Steel Path survival or something.

This has TWO Umbral Formas. If you're looking for the ONE Umbral Forma build, it's still around. I'll link it below. Why have all three Umbrals? I don't really care about Intensify--although it does help with Gloom or whatever other Helminth power I use--but having all three increases the [Vitality] and Armor for even more tankiness.

**I'd also recommend an Aura Forma if you use this frame for lots of different things.

This build is modded to be fast and tanky. Speed makes a big difference in using this frame for just about anything and not holding up your team. Quality of life. You could replace one of the Gladiator mods with [Armored Agility] for even more speed, but then you'd miss the crit bonus. And you can swap [Enemy Radar] for [Sprint Boost] as an aura for more speed if you don't care about the extra radar, but this is fine. On my relic cracking build, I have more speed.

I use Magus Repair in my operator, so at the start of every mission, I load up on my Negation Swarm (which makes me immune to Status Procs), then jump into void mode for two seconds to fully heal myself. Without Magus Repair, you could do the same much less efficiently with Devour.
(Note: With Arcane Grace and how tanky he is, I usually don't even bother healing myself with Magus Repair at the beginning anymore, even on Steel Path, because I'll heal up in no time anyway because of the arcane.)

(Old Note)
After Helminth, I replaced Sandstorm with [Firewalker], which gives me more speed for 30 seconds when needed, cleanses status effects of myself (if I'm afflicted for some reason. Again, Negation Swarm) and teammates, and provides some crown control. I have another build like this where I replaced my 3 with [Khora]'s Ensnare for doing high level Disruption. I have a third build where I replaced my 3 with a (very basic) Resonator from [Octavia] to help in unique defense cases where I'm alone, like the Void Raider mission. (Replace [Gladiator Aegis] with [Stretch] if using Resonator.) The vast majority of playtime, I use Fire Walker.

(New Helminth Note)
Gloom is it, baby. This is the main power. Inaros is my main--my comfort frame that I can use for anything--so I have several different Helminth configs, all replacing his Sandstorm. Gloom is the main general-everything build. It's also for max tanking. I also have an Ensnare build for Disruption, a Resonator build for Defense Objectives, a [Firewalker] build for extra speed when cracking relics, and a Banish build for SP Rescues, Arbi Defense, or Baro defense.

This build gives you EHP of 27,411. When Arcane [Guardian] is fully activated, that bumps up to an amazing 50,699. Ridiculous. And that's NOT COUNTING the regeneration from Gloom and Grace. With the extra speed and status immunity, this basically becomes a very comfortable frame for getting anything done. With Magus Repair and the ability to heal yourself at will without energy, you're invincible unless you try to die on purpose. Or, maybe, unless you stop to stare at your map for a minute then check Facebook while standing in a radiation cloud, lol.

• Dessication is for stunning exceptionally tough targets, like Steel Path Noxes. Not needed, but makes for quicker killing.
• Devour is to heal yourself using an enemy. I don't use it anymore because of two other healing abilities on my build: Arcane Grace and Magus Repair. If you really need to, you can also use Devour to give yourself some invincibility time while eating an enemy, if you're overwhelmed for some reason.
• Gloom slows down all enemies, including Acolytes and liches, and gives you and your nearby teammates vampiric regen.
• Scarab Swarm with Negation Swarm augment makes you immune to status effects. Basically to avoid knockdown from Ancients and self-stagger from your explosive weapons.

The only downside of this build is that his powers are all at base level and not very interesting. Some people think that's boring...? This is a build for using weapons and stuff. Kind of a general do-everything setup, and it's really good for that. YOu can get very specialized with different Helminth builds, which have little tweaks here and there for more range/duration etc., but you're mainly a weapons master.

Here's my older Umbral Forma build from back when I had just one:
https://overframe.gg/build/95422

If you don't want to use Umbral mods, here's a more basic build without them:
https://overframe.gg/build/95421

If you want to use the Umbral mods but not the Umbral Forma, you can add a Vazarin forma (one of the Gladiator mods) and replace the aura with Steel Charge.

If you want to see my oldest (basic) Inaros Prime build before I made him faster, here it is:
https://overframe.gg/build/76183