NOTE This is not my main [Inaros] build anymore. I've updated it to make him a lot tougher and a lot faster. I use him for all 'main' stuff, lich hunting, and anything more serious:
https://overframe.gg/build/95422
My [Inaros Prime] 'main' build, created back when the Prime came out and using the Umbral Forma from Nightwave. I would have put an Aura Forma in there instead of changing the aura to Vazarin, but I didn't have the Aura Forma I thought I did at the time, so just forma'd it to take [Physique]. I'd recommend a universal Aura instead, using this as a main.
This build is very simple and combat focused instead of ability focused, so all ability modifiers are 100. Therefore, there isn't much energy and there isn't any extra strength, etc., so when replacing Sand Storm with another subsumed ability, you need to keep in mind that the ability needs to be cheap and not rely on increased power/whatever. [Nezha]'s [Firewalker] turned out to be a great quality of life increase. I also considered Mesa's Shooting Gallery as something potential for disarming Steel Path enemies. Pull/Shock would also be decent to temporarily throw off attackers.
- Desiccation to stun opponents and use finishers.
- Devour to emergency heal when there isn't another way. Also to turn invincible for a breather in high-level stuff.
- Fire Walker to go faster in general gameplay and crowd control a little with fire.
- [Negation Swarm] to add armor and become immune to status effects. (No getting pulled down by Ancient harpoons) Use Magus Repair coupled with [Negation Swarm], and you never need to worry about healing.
Edit:
Since putting this build up, I went ahead and put on an Aura Forma. After ranking him back up, I first put on [Steel Charge], because I mainly play this frame as a tanky melee fighter. Dropping [Physique], though, lowers his HP from 7xxx to 6xxx, but he's still very tough.
Further Edit:
I've been doing a lot of lich hunting lately, and find that Aura Forma very useful on [Inaros]. A lot of times, I use [Corrosive Projection]. Sometimes, depending on what I'm doing, I use [Loot Detector] or [Sprint Boost] (great for just getting around effectively coupled with Armored Agility and Fire Walker). Aura Forma is definitely worth it here.
(Updated build is here: https://overframe.gg/build/95422 )