MT TM Tungsten armor with Forceful Innervation:
https://underrail.info/build/?HggDAwkDDgYAAAAAAAAAUgB8AHNuD1BVwqBGwqDCoCgAT2JQK8K_LD0qZV9VwoQIwojChyFmwrjCt8K8w5zDlsKewp3CrsOZbOKitQLipbIC4qyDAuKwuAXisLkE378MT TM TiChrome/Super Steel variant with 12 Int (lower for more Wil or not as you wish):
https://underrail.info/build/?HgcDAwkDCwoAAAAAAAAAUgB8AHNuD1BVwqBGwqDCoCgAT2JQKyw9KmVfVcKEwojCh0UkCMK4wrRmw5bDnMKewp3CrsOZbOKitQLip4IC4qyDAuKwuAXisLkE378TC PK TiChrome/Super Steel variant with 17 Wil 6 Int:
https://underrail.info/build/?HgcDAwkDDwYAAAAAAAAAUgB8AHNuD1BVwqDCoMKgRigAT2JQKywFKmVfVSHChAhFJGfCu8K3ZsOcw5bCnsKdwq7DmWziorUC4qeCAuKsgwLisLgF4rC5BN-_This is the third time I'm making and playing a build in this style, so I feel it's refined enough to post. What this iteration has compared to my last two is the addition of Forceful Innervation, freeing up stat points from Int to put into Wil (since tincans don't have problems with lack of skill points) while still having more options overall with spell slots. You can use a high Int edit or opt into TC PK instead of fiddling for FI, but all that Int does aside from spell slots is give you useless overflowing skill points.
Starting stats are 6 Str, 9 Con, 10 Wil, 6 Int. You'll need to put two points into Strength to be able to wear tungsten armor or only one if you prefer TiChrome/Super Steel (don't worry, you won't have to be eating rathound barbecue constantly, read on), and the rest into Willpower/Intelligence; the order is up to you. I'll personally allocate my first point to Wil then the next two to Str.
Before finishing Depot A, you'll be using Survival Instincts as an under 30% HP glass cannon to grant you a massive boost to damage that's much needed on Dominating. Certain fights (like against mutants) will require you heal up to 100% HP beforehand however, if you don't want to cheese with bear traps. After Depot A, SI becomes more of a bonus at low HP rather than a mainstay, and Psionic Mania and Focus Stims take over for your crit chance needs.
Always max Metathermics/Thought Control and Temporal Manipulation/Psychokinesis. MT/TC will let you deal with nearly all NPCs, and TM/PK provides Distortion/Electrokinesis against robots (and bosses in the case of TM). Leave whichever schools you're not specializing into for later in the game. In my FI build, I'm only maxing TC as a bonus tool in Neural Overload so I don't have to reload on fights against Doppelganger spamming TCunts. No reason not to take a little bit of Persuasion with high Wil and its Mercantile synergy, 20 base by the time you reach Junkyard will be enough for the early game. Since we're on that topic, Mercantile is extremely important for getting high quality components, so get it to 79 base ASAP: with the Persuasion synergy and Jon's Special, 105 effective Merc is reached for the highest special merchandise check. Max mechanics, electronics, and tailoring until their respective thresholds as well, since you'll be crafting metal armor and psi headbands. Whether to get Pickpocketing or Hacking first is up to preference; I like Pickpocketing early on far more than Hacking, but I usually leave it around 80 base until I have free skill points and switch those points to Hacking or something else. You *could* get Lockpicking instead of one of either, but it's the second worst Subterfuge skill, especially on high Strength builds that can crowbar vents already.
For Depot A, get siphoner leather and eventually mutant dog leather armor and boots; acid threshold will let you tank through many attacks in this dungeon; the obvious choice really.
Once you deliver the circuit board, rush to Hecate Research Outpost and get the Power Glove. As full psi builds don't have any good weapons to equip until Expedition, this frees you up one stat point from Strength. The other slot will eventually be occupied by Hoddurform when you're TC/PK or Spirit Staff if MT/TM, and you'll switch to it when attacking. A single caveat: if you end your turn without the Power Glove selected, you'll have a small action point malus on the next turn due to not meeting the metal armor Str requirement, so don't forget to switch back! Don't be afraid to switch at the start of the turn though, as the malus won't affect current AP, only maximum AP.
Now that you can wear metal armor, craft yourself a tungsten (or TiChrome from Blaine) one with a regenerative vest. Not only is it tankier than a sturdy vest, it also powers your spells through Hemopsychosis. Reinforced metal boots with high density padding is also a given, but in the case of TiC/SS, soft padding and springs will benefit you more. You also should have crafted a MT headband with psi cost reduction and crit damage, as well as a TM headband with a Distortion filter in case of mass robots. Doctor's Belt is the best to wear with all the meds you'll be chugging.
Juggernaut is taken at level 12 since that's around the time you obtain the Power Glove. If you want to do the Super Steel armor variation of the build, Optimization is replaced with Armor Sloping, and you take Neural Overclocking at level 30 instead. LoC is also switched out for Nimble in the MT TM version. The tattoo is up to you, I like the QoL of Fatso myself. Protectorate should be better if you want something more substantial though.
Your first four spec points must go on Hemopsychosis cooldown. The less you have to rely on the low regeneration, low max points of psi, the better (especially so if you're playing with Forceful Innervation). After that, maxing health cost reduction helps out quite a lot. Psionic Mania and Premeditation cooldowns + LTI and Stasis will let you have effectively a second "alpha strike" turn. Thermodynamicity really helps with AP usage, sometimes so well to the point you're left with no HP to cast more spells with some free AP. If you're playing with Armor Sloping, that specialization's best gotten as soon as you finish Hemopsychosis cooldown. And there's not much to say about TC PK, as it's very straightforward.
If you're wondering how exactly to get Forceful Innervation on a new character, and also get the content added after Legacy like Booth or the Utility Tower, it's not too complicated. You'll have to make a new character on the Legacy version, go get the psi pill, save, then load that save on the current version, which will give you FI. Then, export the character and start a new game with it, and optionally reroll if you get Coral. And of course, unless you want to cheat, don't grab anything before exporting because it carries over.
Edit: replaced Continuum Ripple for Locus of Control, as it lets you have psi inhibition immunity without the need for a Reinvigorator.
Edit 2: replaced Fight Response for Psychoneural Optimization. At level 30 you'll almost never start a turn under 25% HP, and Optimization slightly helps with Plasma Beam spam when you have the Cyclop's Eye. Added siphoner leather armor suggestion as that helps fight your first mutant dogs before you have their leather. Also moved spec points from Thermodynamicity to max Hemopsychosis cost reduction, as you're not worried so much about AP cost but health.
Edit 3: added TC PK version, it's easier to play and more straightforward than MT TM due to not needing as many slots.
