Final Boss struggle (big spoilers)

[Yonaiker]

After killing him 2 times in the past without problems this time feels unfair; my build is focused on sustained damage (pistol build with metathermics) which gave me positives results on past quests (rathound king, arena, free drones), and now at Tchort it feels very weak due the nature of the encounter:

- My latest playthroughs against it I had enough burst damage to kill him with just one mutagen tank destroyed. (Pure PSI and SMG build)
- I can only manage to destroy two mutagen tanks of the right side, having a pistol build forces me to take a long walk to get near them, but for this one I have MKV grenades which helps the range issue. Trying to get the remaining tanks is futile due the heavy tchortling spawning, running out of health hypos and constant harassment of the tentacles (Cryokinesis, thought control and acid for this one)
- If I rush to Tchort with only two mutagen tanks and throw everything I can't make enough damage before I get overwhelmed by its minions. (Inmune to Pyromaniac, toxic gas contamination effect, biocides grenades help but I drop quickly)

I don't recall getting overwhelmed so fast by its minions too quickly, my character doesn't have enough strength to wield a sniper rifle to make a quick work of the tanks and have limited movement points, maybe I just built my character wrong but I made it so far so it could be hardly the case.

This is my build: http://underrail.info.tm/?build=AwGloJgVhAWECcIYwIygBzJKgzG-MIvGcHQs0XUVaHO20omi5nELVAdhAgl9whqQrLiSxBseLABsyVCC5YEC9KiA
Weapons: W&S Revolver/Phase Gun

[Lucifuga]

That is some excessive throw skill just for nades.
May as well put it to good use.

This will require stocking up on those MKVs.
The storage room needing electricity to open up had about 20 nade cases while the Tchortists sell the powder components. Should be able to make yourself ~7 in a single stock spawn.

Both bottom mutagen tanks can be destroyed via nades within the first few tiles of the ladder.

Your first step should be entering the nearest safe room and losing the aggro there in order to exit combat. The tentacles should then rearrange themselves. Two should be on your right and one up north.

Now from here your next step is to go back to where the ladder is but end your turn on any of the 5 bottom tiles. The closest tile from the room will need ~70 movement points to reach after having gone outside. A jumping bean drug and/or adrenaline will help if you can't make it.

Having successfully reached any of the 5 bottom tiles prevents the tentacles from rearranging themselves. The tentacle up north can't hit you from here so you can now consider these 5 squares as sanctuary. Pass the turns and exit combat once more.

Now the grenade tossing starts.
Each tank will take ~5 nades to destroy. Manually enter combat for each throw. Do remember that you must end your turn on the bottom 5 tiles for smooth sailing. My advice is to destroy the bottom right tank first. The noise from the nades will only attract two tchortlings however they won't actually aggro on you. Instead they'll try to investigate the noise but the closest they can get isn't near you. The Mouth of Tchort will probably aggro but he is like wet paper.

Onto the left mutagen tank.
The goal here is to attract the two tchortlings from the right side of the map over to the left. With all 5 tchortlings being on the left side of the map taking out the top right tank is much easier as well as hammering on Tchort. I was able to do this by going to the tile on the top left of the ladder and throwing the nade so the very edge of the blast radius hit the top right corner of the tank. Go back to your safety tiles and you should see the tchortlings from afar as they travel to investigate the noise. They don't have the needed range to spot you.

This is incredibly cheesy and fairly arduous but its a free two tanks and makes the fight much much easier.
If you still can't close it out you can try luring the tchortlings from the left to the right side with nade noises while keeping out of range in order to reach the final top left tank. Experiment a little.

Luck of best

[Yonaiker]

That was a good strategy, I managed to blow out the two first tanks while the RNG curse causes only the acid tentacle appear and attack me even standing a the bottom tile, but the real issue are the freakin' tchortlings still coming to my position (panic room), 4 of them appeared (two sowers one devourer and a scanner), opened the door and destroyed me there.

Hell... looks like I'll have to cheat this one, I really love the theme of this fight but it could use some tweaks, only builds with very high spikes of damage in a few turns (energy pistols criticals, full psi, burst attacks, snipers) can make it without much trouble.

Still thanks for the help, its inmunities only make it worse.

[Lucifuga]

In my test I had 0 throwing so my character consistently over shot the grenade past the distance limit. This made it so the tchortlings never bothered me.
My bad

Tinkered a bit more and found that throwing a gas nade on the right hand side of the intersection prevented the AI from checking that avenue when investigating the noise.

I find images help

Recap

1st Image
Make it to the door

2nd image
Move to the top right corner of the safe room
Mouth of Tchort will probably pay a visit. Stay put in your corner, kill him and then skip turns until you can exit combat.

3rd image
Enter combat, move 1 tile down and 2 tiles left. This is so the top right tentacle won't move.

4th image
You'll need 102 movement points to make this run but 100 will suffice. Popping an adrenaline shot should be enough so that your character is far enough inside the tile that the tentacles won't move.

5th image
This is how it should look having succeeded.

6th image
Throw a gas nade out here. Wait for it to expand enough to "block" the path and commence the nading on the bottom right tank.

When starting on the left tank I wouldn't use the gas nade to block the path as drawing over the tchortlings from the right side was consistently safe in my test.

[Yonaiker]

Well I figured out how to not attract the attention of the tentacles while destroying the tanks. After that I decide to rush to Tchort while covering the path with biocide to deter any Tchortling but they still charge at me through the gas, my only inconvenience in this fight is a Damage Race one; destroy the eye as quickly as possible because the tentacles will erode you pretty fast (Damn the thought control one), and their regen is still strong enough to stay alive, that would explain why my previous playthroughts were just a breeze, hit hard 'n' fast and done.

I hope Styg just tweak a bit this fight for slow but steady damage builds (pistols, knife, crossbows and poisons) or characters with low constitution, not asking nerfs btw just making it more viable.

[Lucifuga]

This is unreliable but I've got another possible route to victory for ya

The goal is to gather up enough stealth granting gear that totals up to 86 or more points. With 86 effective stealth one can successfully avoid all enemies (excluding Tchort) in the final fight.

The checklist:
Cloaking device blueprint   (No clue where to find one in DC)
Electromagnetic Deflector
Electromagnetic Field Stabilizer
Plasma Core

Crafted Cloaking device + a ton of batteries
Stealth granting armor
Stealth granting boots
TNT Charges (minimum 2)

Cloak is essential as it will be the most stealth granting piece of gear your character can make but is completely dependent on the RNG your version of DC rolled with components. The most crucial part is the Electromagnetic Deflector as its quality determines the stealth bonus. With a quality of 130 your character can gain 64 stealth with the cloak alone.

Cross your fingers and head back to the storages in search of high grade components. The back room of the Power Station boss also holds various electronic parts.

Onto armor. If the faceless storage doesn't pan out with good stealth armor the Tchortist merchant sells both riot gear and vests. Eventually you can wait out a good stock spawn until he has some nice overcoat gear. The armor piece should net you ~20 stealth. Rathound Regalia gives 25.

If you are just shy from the 86 total you can buy some rathound padded (black cloth) boots from the Tchortist as well. They typically give 6 stealth.

Do take armor penalty into account as it will reduce the stealth bonus of all worn gear.
The cloaking device is thankfully excluded.

Finally with the needed stealth go into the fight and exit combat on the safe tiles, equip your stealth gear, enter stealth and turn on your cloak. Head for the top tanks and place a TNT charge to destroy them. You'll probably want to keep batteries on your cast bar as you'll need to frequently recharge the cloak throughout this. The top left tank will be the hardest to blow up as the Tchortling is entrapped in the corner by gas and won't be (rare times it will) lured out with noise so it'll be difficult. With enough luck though it won't bother you while placing the charge.

After blowing up the top two tanks exercise the nading strategy and you should finally have enough of an advantage to beat Tchort. I advise to go for the top tanks first as the constant damage amplifies with each one that is destroyed. Healing up will take you out of stealth.

Here is a strat for blowing up the top left tank if you can't manage it.
Exit combat on a safe tile -> place TNT charge to your right -> stealth and head for the top left tank -> once the TNT explodes the tchortling will go towards the edge of the gas cloud -> pass it by as it move towards you and place the charge (entering combat helps you not bump into them)

You should be able to make it by doing this. Head back to the safe room while avoiding the oncoming tchortlings, heal up and head for the top right tank. Entering combat gives you the push to get you by the tentacles undetected.

I must reiterate that this is an unreliable method to beat Tchort and it may not work out for you as there are many variables beyond one's control but it is a feasible way to win.

[Yonaiker]

Finished the playthrough, will take a vacation while Expedition is on the way, xbow poisoner is the next on my list but will wait for the expansion hoping crossbows are more viable on Deep Caverns and Tchort.