LF an Unstoppable Force

[Valok]

Before we get to the meat, a bit of context:

Some good time ago, due to some problems in life, I had to stop my (rather advanced) playthrough (I had done I'd say 60-70%? of the main quest/side quests and I think I was 60%? done with the expansion). When I finally decided to come back later I was a bit put out due to losing my save and having to redo the whole thing, so I essentially abandoned the game and went to do something else. However, recently I decided to come back and finally 100% it but for this though I want to avoid some of the headaches I went through in my first playthrough, and I'd like to have a character that will offer me more fun than my first.

What I didn't like was having to resort to 'cheap tricks' (i.e doing the best to abuse the AI or location, or having to resort to traps/etc) or save scumming all the time the moment one thing or another goes wrong or I'm met by a new circumstance because the only way I could get through a fight is if I'm doing the jump on the enemy (i.e the true power of the character does not lie in himself, but rather in a completely external actor that gives him perfect clairvoyance and time traveling). What I need is a true juggernaut.
He can rely on stealth to begin a fight, sure he will use grenades/stims/etc when available, ideally I'd like him to use psi for the 'special flavor' it gives to the character (though its not necessary), but all these things should be extras, he shouldn't NEED them to actively fight groups or survive engagements - no matter how long they could be. Ultimately, what I want is staying power.

As an example; imagine a frontal assault on that military base. From my searches what I've seen is people poping some CD's on stim/skills, killing some enemies, and then immediately running for cover because the character can't seem to survive more than 1 person hitting them. I'd like to avoid this as much as the game allows me to. Ideally the fight would start, and the character would just keep mowing down enemies one after another, even if all its best stuff is still on CD. The most recent build that caught my eye a bit was this one bellow. It does show some staying power and, thematically, it looks cool, but as you can see it still has some of the things that I'd rather avoid if at all possible.

Is this the best that we can get out of a character? Or perhaps someone could pinpoint me to another build that's more in line with what I'm looking for?
/watch?v=IAGwGonhobw

[Kekus Maximus]

This is doable, yes. The example in your post has about 0 actual staying power and relies on running and also TM being OP af. In other words any build that can reliably kill at least 2-3 enemies per turn will easily dominate the game with 3 will 70 TM ^tm. It is definitely very strong, but it just can't allow enemies to even breath on them; EMPs are most likely equal to instant death.

Here's my recent leather/metal gloves build. Not quite fitting, lacks raw power until late game, but still it can explain one way to approach this, sort of:
https://underrail.info/build/?HAcPCAUDAwUAeADClijClngAVS0AAAAAAAAAAAAAAAAAJDkmIEEGEgdDCQMxTjzCs0vinY0J4p-EAeKmrgPfvw

I didn't pick Fancy Footwork on purpose. The philosophy behind this build is simple - if I can't run away, and can't kill a lot of enemies per turn, I have to do everything in my power to debuff or disable enemies, so even my mediocre defences are too much for them to overcome.
It's not tanky at all, but it can stay surrounded by enemies for multiple turns, thanks to specced Wrestling. It lasts two turns, that means you can refresh it with 1 or 2 hits, just ~5 AP. On my belt I almost always had cave ear poison throwing knives and throwing net, and the last belt slot was either for flashbang (rarely used), or molotovs, which i could throw under my feet while being in the middle of a crowd, or black dragon poison knives to disable psionics. Or sometimes cloaking device to further boost evasion. High evasion and antithermic leather armor almost completely negate grenades. Incapacitation from pneumatic hammers are really hard to resist, so most organic targets that survive after being hit by one will be disabled, usually till the very end of combat. Staying near disabled enemies prevents others (except Lunatics) from using bursts, grenades, AoE psi and flashbangs. Crippling strike is very good against snipers and some AR and shotgun users as well, sometimes crippled snipers don't have enough AP to shoot, but if they do, they have a huge accuracy penalty. Five CON is not too little, not too many to hurt damage stat; on 20+ level and with some mid leather armor and a good shield it's possible to more or less reliably survive a single sniper crit, if you let them land it; at level 20 I gave the first turn to Carnifex, and successfully survived with ~35-40% HP. Regenerative vest is a great choice for general combat, though most of the time I preffered infused rathound leather for crits and fire protection. High DEX and 8 agility means even if I fuck up stealth, I still get my first turn pretty often. Lastly, Uncanny Dodge allows to completely ignore melee enemies and focus on more dangerous targets instead; and it was a real MVP against faceless gaunts in DC.

The lesson of this playthrough was - don't fuck with Faceless before the endgame, it's not worth it. Foundry Faceless at level 16 was a single hardest fight for the build before Expedition.

In the end it is a very solid build, despite lacking a little in offence; however I struggled in DC with Faceless base so much I had too cheese it with gas grenades. On the other hand, if I faced the Faceless (badum-tss) after last boss, I would probably had a much better chance.

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I also posted Cryo Tank build a while ago:
https://stygiansoftware.com/forums/index.php?topic=8799.0
This is, in essence a very fat yet evasive psi "sniper" with occasional powerful crits and 2 very good AoE abilities. Definetely needs some tweaks tho, less WILL, more AGI (because 6 is not quite enough) and 1 additional point in INT, needs more base psi points as it runs out very quickly; I also recommended a lot of very optional items and to spec in Hypothermia, but now I think it's a complete waste of time and points, and Hypothermia doesn't work on last boss anyway.
I stormed a pirate base all on my own with this build, and only in one location I had to reload multiple times. This build has to break line of sight from time to time, and since it's a Psychosis build in some fights I had to do nothing for 1-2 turns due to huge psi costs, it can barely deal with robots until at least level 16; nevertheless I still think this is the closest I've done to your request.