As some might know at one point developers did a silly thing and introduced considerable limitations on psi users. This effectively locks out godlike cave wizards out of new content while constantly forcing psi users with never game version to take psi inhalant for psi point regeneration and probably numbs the pain of knowing that some pipeworkers who wake up at night screaming because concept of unlimited inventory exists and preferable for everyone (especially for such a long game) decided that after 5 years after release it's imperative to take unwelcomed, unasked change to worsen the experience of thousands of players because one of many overpowered builds is a bit self sufficient, while also limiting their effective psi abilities up to 8 (9 with specialized headband) out of 38 (though you still can swap them between battles, but it will deplete all your psi point and psi reserves), making additional psi schools less desirable and more psi abilities not used ever again.

While you can enjoy most of the content with convinient psi by playing legacy 1.1.1.6 I would not recommend it simply because 1.1.5.9 introduces enough content and psi abilities to make legacy obsolete and sadly right now there are no mod to fix it and we yet to see if someone updates cheat table to include unlimited reserves.

While the latter would be appreciated not only by community, but by any sensible sentient being, it's understandable that not everyone is equipped with proper skills and time for such thing, so it's up to you to decide which half baked choice to make. If you decide to stick with 1.1.1.6 you can use this build[underrail.info], which follows the same approach as the current build (if you decide to roll with JKK in Core City you can take some point from persuasion).

Heavy duty appears to be not as impactful for this build (no new feats for psi), but you might encounter new items worth considering and skill checks/effective limits might be affected.

Overly optimized full psi tranquility expedition build[underrail.info] is based on my normal 1.1.1.5 to 1.1.1.6 playthrough with Expedition DLC, some wiki[stygiansoftware.com]/destroyor info and superficial research of 1.1.5.9 and should work as expected on maximum difficulty. If you want different psi tranquility approach you can build on sheepherder's agility based build[stygiansoftware.com].

Ultimate goal was to accommodate superior fighting and crafting capabilities while taking in account convenience. If you find some problems while taking in account my design choices please let me know in the comments.

To make the highest skill checks work you'll have to collect and craft stat boosting equipment/food/medicine and accurately follow Jack Quicksilver questline (starts at SGS LvL 3 Commons and Cantina) to the end. At LvL 8 your character stats will probably look like this[underrail.info], at 20 like this[underrail.info].

You can get better results[underrail.info] by rolling with JKK for their best stat boosting equipment (+45 persuasion) and working with Institute of Chort for Electroinvestigative Belt (+15 electronics).

Build can be optimized further[underrail.info] by obtaining Remote Control Energizer Glove (+10 hacking/electronics, look for Phreak[www.stygiansoftware.com]) and getting Bespoke Buckle Shoes (+20 Persuasion/Mercantile, look for Luperchaun random March event[www.stygiansoftware.com]), but it's kind of pain and there are many unaccounted skill and other stat boosting equipment (like boning knife[www.stygiansoftware.com]) and food/medicine consumables (like drinks from waterways Drag 'n' Drop[www.stygiansoftware.com] bar) that keeps appearing and makes it harder to build for "the best skill values of all times", but fortunately for now abilities and feats remain the same. If you overinvested in skills and it bothers you, they can be adjusted by using cheat engine table.

Strength 3 - a bit more carry capacity is mostly useless and without maxing Corporeal Projection doesn't worth it

Dexterity 8 - at first glance it doesn't look so good, but it allows you to get Fatal Throw feat + you get quite nice bonus to initiative, 4 useful bonuses to skills and minor stuff like better early fishing and lower AP cost of light weapons.

Agility 3 - you might think it's good, but you get more points for stealth with dexterity, you don't need dodge/evasion at all, movement points are overrated for psi and AGI checks are disappointing.

Constitution 3 - it's nice, but you rely on being full hp, so it's mostly useless (even counting Fast Metabolism)

Perception 3 - while detection is nice for spotting traps and stealth enemies (like infamous crawlers) all thing considered it's straight up useless for psi. It also effects finding secrets, but they don't give anything that you can't get otherwise and you still can get them by knowing where they are and having enough bonuses (equipment, food and medicine can give you up to 17 effective perception for secrets). If you really want to hunt for secrets either go for Perception build (makes most sense with Assault Rifle, Crossbow, Sniper Rifle or Shotgun build) or cheat by getting yourself more perception with cheat engine table.

Will 10 > 16 - your psi damage, persuasion, resolve, psi regen and some checks rely on it. Too good to not max after getting 12 intelligence. 18 Will gives you more damage, but difference is so negligeble that it's not even worth discussing.

Intelligence 10 > 12 - all crafting, hacking, psi regen and some checks. 9 for Philosophy III trait, 12 for 8 psi slots.

Offensive skills are rather useless for full psi except of throwing (71+). While full psi doesn’t really need to use it, your throwing knives AP refund is amazing while grenades are useful from time to time (you also obligated to use grenades at least twice throughout the game). Maxing throwing using skill points from stealth will double the damage, but because you mostly use it for AP refund it's questionable idea since not that many enemies have 600+ health even on dominating difficulty.

Defensive skills are rather useless since our motto is kill before getting hit and over 90% of enemies will miss almost all the time with active pseudo-spatial projection ability.

Subterfuge

Stealth 128+
Doesn’t directly work with psi, but for skill dump it’s fun and useful to gain better position, avoid fights, steal etc. With Rathound Regalia, high level tabi, cloaking device and All-in food you can lend on 300+ effective skill.

Hacking 60
Constantly used for loot and quests. Lends you on 130 effective endgame check with Lemurian engineer suit, Underpie and hypercerebrex medicine (tools don’t count).

Lockpicking 63
Constantly used for loot and quite useful for quests. Lends you on 130 effective endgame check with Lemurian engineer suit, Eal sandwich food, jackknife and huxkey.

Pickpocketing 27
Used for extra loot. 38 effective with Eal sandwich or Underpie can make certain change of events in expedition for Aegis, without it enough for pickpocketing All-in and other cocktails from Drag 'n' Drop bar on water. You might want slightly more on oddity exp or some unexpected pickpocketing.

Traps 31
Useful for noticing, picking up and laying down big surprises. Lends you on 95 effective skill with Lemurian engineer suit, Trapper’s belt, Jackknife and Eal sandwich or Underpie which is enough for picking up most and laying down all mines that you can craft.

Technology

Mechanics 62
Used for crafting and useful for quests. With crafting bench for your Core City home, Underpie food and hypercerebrex medicine lends you on 146 effective skill which is enough for quests and should be enough for even 188 psi related crafting.

Electronics 73
Used for crafting and useful for quests. With crafting bench for your Core City home, Underpie food and hypercerebrex medicine lends you on 170 effective skill which is enough for quests and should be enough for shield with 164 quality high frequency modulators.Raise it if you want to craft better shield and have ingridients for it or lower it by ~10 if you fine with weaker shield (you don't really need it anyway)

Chemistry 6
Just for extra crating. 20 effective with crafting bench for your Core City home, Underpie food and hypercerebrex medicine for gas grenades and some bio vests, only 15 for psionic inhalant and TNT.

Biology 46
Essential for crafting because of hypercerebrex medicine. With crafting bench for your Core City home, Underpie food and hypercerebrex medicine lends you on 100 effective skill for Super Health Hypo.

Tailoring 70
Crafting only. With crafting bench for your Core City home, Underpie food and hypercerebrex medicine lends you on 151 effective skill which should be enough for 188 quality tactical west.

Psi

Obvious maxing out for damage while keeping temporal on 70 for highest ability because temporal in general doesn’t scale much. Thought control might look weak, but it has very good stuff that works great against almost all enemies.

Social

Persuasion 38
Very nice to have for quests. Hard to calculate throughout the game, but will get you to 110 effective skill with Underpie food, Heartbreaker serpent leather boots and armor.

Intimidation
Mostly exists for roleplay and skipping quests. Hard to calculate throughout the game, but If you really need it steal 7 points from skill dumps like stealth and use Under Pie, Death’s Grin, Tchortist Robe, mutated dog leather boots or tabi, bullet or shell trap belt and Butcher’s Cleaver or expedition natives weapons to lend on 100 effective.

Mercantile 55
Essential for crafting and nice for quests. With Underpie food and hypercerebrex medicine lends you on 110 skill which is enough for all quests (except max prices for expedition loot) plus best traders inventory and price in all shops. If you really want up to extra 8000 charons out of 36250 possible from expedition loot, raise base mercantile by 16 to lend on 140 effective skill.

Skill dumps like throwing over 50, stealth and very high crafting thresholds are used to dump excessive skill points and can also be exchanged for something like more persuasion earlier, more
crafting, pickpocketing, stealth, throwing or temporal manipulation.

Paranoia and Trigger Happy are here to combat one of your biggest weaknesses - initiative and detection. Saves lives and your time.
Tranquility because it’s tranquility build and action points are the biggest limiting factor
Cerebral Trauma Improves one of the most efficient psi abilities
Force user helps at lower levels and unpleasant situations
Premeditation essential feat for any psi user
Meditation multi psi is multi hungry
Psycho-neural flexibility multi psi is multi hungry
Locus of control saves from stuns and helps with applying mass mental disabilities
Psycho-temporal acceleration free action points
Fatal Throw Cherry on a top for this build. Allows you to finish enemies and refund AP.
Throwing Knifes expirience can be improved with Knife Thrower's Glove[www.stygiansoftware.com], also works with Shock Shuriken
Neurology multi psi is multi hungry
Thermodynamicity more thermal explosions per round (doesn't work with plasma beam)
Neural Overclocking better crits
Increased Will essential psi stat
Advanced Psi Empathy multi psi is multi hungry
Mantra multi psi is multi hungry

Pretty much all first 2 feats are useless for this build, so my choice is to get something consistently useful - 12 initiative and some detection/crit chance reduction. If you really dislike those choices you can swap them for Nimble, Snooping, Clothier (get 15 tailoring at the start) or Doctor (get 15 biology at the start) for measly gains.

Force user and Thermodynamicity are also optional feats, that can be swapped for other psi feats like Pyromaniac, Psychostatic Electricity, Mental Subversion, Psychokinetic Elasticity. Non psi damage related feat options include Remote Surgeon - throwing knives do more damage, Quick Tinkering - setting traps in fight, Three-Pointer - more damage for grenades and Grenadier - less cooldown for grenades. Also Expanded Psi Capacitance or Ballistics for measly gains.

Tranquility +10 enables x3 Electrokinesis or x6 neural overload per turn and more
Premeditation: Cooldown +2 to end more fights on turn 3 by starting fights on expiring premeditation
Fatal Throw: Action Points +3 now you refund at least 11 AP after killing with throwing knive.

Or you can complement your Tranquility +10 by enhancing metathermic action points use with Thermodynamicity +5. If you really like setting traps during fight you can get Quick Tinkering: Action Points +5 - now Quick Tinkering doesn't consume AP.

In case you lend on playthrough with Booth[www.stygiansoftware.com] your primary choice should be Shadowlith. It's somewhat endgame option (Basically you need to end something before you complete expedition. Don't forget the Ethereal Torch[www.stygiansoftware.com]), but it's a good bonus and sadly The beast and Anarchy doesn't work with psi. Alternatives are lacking, but if you really want something else I would consider Black Crawler, Fatso, Abomination or Drifter.

Even though you gain 10-20% psi cost penalty for having 3-4 schools I still recommend using most of them for your usual all around set since eventually you will have sufficient psi and all of them are good for different, but regular situations. My usual set consist of:

Psycho-Temporal contraction is an obvious choice for any build and should be used all the time as long as you have enough spare psi.
Neural Overload - cheapest silent attacking ability that combines with ability below
Mental Breakdown - 3 round silent stun that also applies a nice bonus to neural overload. Usually used with Locus of Control ability
Pseudo spatial projection - extremely useful ability that usually allows you to ignore most attacks except grenades, mines, environmental stuff etc. Because of 5 turns duration should be applied before starting a fight.

For most situations 4 of those are good enough, but you still need something against robots and more options against distant crowds, so use this.

Electrokinesis - with full tranquility specialization you can stun for 1 turn almost everything 3 times per round and still deal damage, especially against groups
Electrokinetic Imprint - essentially almost free psi trap. Deals huge damage and stuns targets for 2 rounds, but what is important is that you can set it up before a fight and it’s very cheap both action and psi wise
Plasma Beam - one of the best damage wise and probably the coolest psi ability with the biggest range
Cryokinetic orb - great area damage with additional frosting and bleeding. Gives action point discount to pyrokinesis with Thermodynamicity feat

Honorable mentions for switching (or additional headband slot)
Frighten and enrage sometimes work better than mental breakdown, but sadly first wastes your time and second wastes your loot
Telekinetic punch, telekinetic proxy and implosion to fight overly thick robots and certain single targets
Force Field for some “ArenaNow and chill” while your enemies are screeching through the wall
Telekinetic Grounding - powerful and cheap enough stun for up to 5 turns
Pyrokinesis - good area damage with running and screaming torches. Gives action point discount to cryokinetic orb
Cryokinesis for additional sniping
Cryogenic Barrier is tied to water, but quite otherwise quite effective barrier
Thermodynamic destabilization pre apply for additional fireworks
Exothermic aura to warm yourself in this cold world
Psycho-temporal dilation to slow them down
Entropic recurrence next turn repeats your last damage with interest against the bulky ones
Stasis single target “ArenaNow and chill”

Head: unless you want to heavy spec on electrokinesis, cryokinetic orb or neural overload get yourself universal one with crit chance and psi cost reduction, it’s the best one overall. Switching before the fight is always an option too.
Suit: sturdy laminated with beetle carapace and black cloth. Bio vest is nice, but get gas mask or bio suit or bio boots instead.
Belt: Doctor's Pouch is the only one actually useful.
Weapon: spirit staff and staff-spear are almost equal in usefulness, but first wastes your mind with constant laughing and second one wastes your reserves when you switch weapons.
Boots: black tabi unless something is wrong with the floor.



Shield made with both 164 quality dual high frequency modulators, 164 quality plasma core and 161 quality efficiency converter. On normal psi doesn’t need it at all, but sometimes it’s handy.



Ninja Tabi Boots with 154 quality black cloth, best you can find on sale. Generally the best for psi.



Cloaking device made using only 164 quality parts. Stealth is fun.



It’s very hard to make a max quality vest so here is one with sturdy carrier 147 quality, laminated panel 164 quality, psi beetle carapace 99 quality and black cloth 154 quality. Very high quality Super Steel Sheet as panel might be slightly better, but it's just too expensive and bothersome to care.



Motion tracking goggles with 158 quality lenses and 162 quality plasma core



Psi headband made with only 164 quality parts



Specialized psi headband made with 164 quality parts (cryokinesis filter 163, but 164 has the same damage)

Other fun stuff



Acid Blob pistol using only 164 quality parts



Incendiary Blob pistol using only 164 quality parts



Cryoliquid Blob pistol using only 164 quality parts



Leather armor with 112 quality mutated dog leather, 164 quality insulating foam paddler and 159 quality aluminized cloth

Endgame craft



Electroshock pistol with 166 quality electroshock generator, 183 quality plasma core, 182 quality high efficiency converter and 143 circular wave amplifier.



Hawker with 186 quality frame



Marauder with 183 quality frame

Why they considered insane? Because normally you have very small chance to get max quality materials on sale and even with force merchant refresh it’s very tedious.

In general difficulty scale can be presented like this:
Easy (I'm not good with combat) < Normal (That's my first playthrough/This difficulty is fun enough) < Hard (I know what to do and I like extra challenge) < Dominating (I know how and want to deal with extreme challenge on every major step of the game with this particular build).

Basically this means - don't start a dominating playthrough unless you already completed normal/hard playthrough with similar build or you are very good with this game.

+ and - keys to speed up your movement and time-based events
F for quick ability menu
1-9 and Ctrl/Shift + 1-9 mostly for tools and premeditation

This game has enough experience (especially on classic mode since it has respawning enemies) and money (for example respawning loot to pickpocket from waterways bar and fishing) to go around so don't care much about it until you need it.

Beware that oddity exp incentivizes to ignore enemies and prioritize quests. It's not really harder, but you might find it less enjoyable.

Find the drill parts aka Depot A can be cleared easier by prioritizing stealth (as high as possible), lockpicking (75-80 effective) and hacking (55 effective).

There are 4 ways to leave starting location after finding the drill parts
1) Free, but slightly inconvenient junkyard embassy elevator
2) Metro. Very convenient, but a bit boring
3) Boat. Very convenient, but a bit boring
4) T.N.T. Northern rocks of lower passages since it opens important root

After leaving starting location main quest is more or less irrelevant, I would even recommend to ignore it until endgame. Also grab jackhammer tool from Foundry mines to remove those pesky rocks efficiently and complete Camp Hathor quest early for a generally good unique item which also allows to ignore the most common enemy in the game.

You need around half of your inventory space for stuff you equally need, but other than that - just use cheat engine table and don't be like those poor souls who waste hours to move their inventories from one location to another. You can also use it to rebalance your skill points if you made some silly mistakes or when testing out stuff/noting skill checks on wiki. If for some reason you can't enable stuff on certain locations/situations try different saves first, enable it, then load your current save (obviously doesn't work with rebalancing stats, do it with your current save and save afterwards). For inventory activate main script, then enable max carry weight mod (you can modify value for even more inventory space), then disable main. Be aware that activating main script heals you. For merchant refresh and jet ski weight mod you have to interact with merchant/jet ski first, so it's a good idea to create separate save where all of it is available.

Recycle Item recipe can make you good money at least up to normal difficulty by crafting Leather Armor from Rathound Leather, then recycling it to make Repair Kits that can be used to repair and sell expensive armor for extra profit.

Destroying factions will cause or halt certain encounters.

If some DLC or just high level robots are dominating your ass try EMP grenade MK III, they stun robots for 3 turns.

140 quality materials are good enough. Some materials might not even scale to that number. Craft it now and stock overly good ones only if you really bored.

Stroll around seemingly big and empty location more often, that's where all those interesting random encounters happen.

At high level (partly applies to lower levels) you usually should start your serious battles with applying Pseudo spatial projection, then simultaneously premeditation, then waiting until it's 5 sec to expire and start a fight, preferably with costly ranged ability. This way Pseudo spatial projection becomes almost free or even free and premeditation will be available at turn 3 when enemies should be very close to death.

For jet ski - since psi is usually better than all jet ski weapons just get yourself Torpedo for speed and don't buy Freighter since almost all jets outside of shop are not sellable.

I greatly enjoyed this game and I will be anticipating sequel with my full attention, but I do hope development team will include more convenience options and exclude late time inconvenience changes from it's list so more players can enjoy it without a headache.