Untouchable Gunpsyker Commando
 Psyker Build - Warhammer 40k: Darktide 

TL;DR: Run fast, be immune to bullets, massive crit & weakpoint damage, suppress/kill shooters & gunners with recon lasgun or engage them in melee with SPEED

Core build concepts:

1. Be immune to bullets
2. Run really fast (+55% sprint speed)
3. Use your speed to force melee engagements and prevent shooters/gunners from shooting you and your team
4. Crit everything
5. Burn specials/elites with your ranged crits
6. Suppress ranged enemies that you can't reach

This build is optimized around sprinting fast and being invulnerable to ranged fire through Stripped Down, Empathic Evasion, and Deflector. This lets you zip around combat rescuing netted allies, engaging enemy firing lines in melee (or suppressing/burning them), being extremely evasive vs melee and ranged, and just an all around powerhouse of melee and range combat through crits and weakpoint damage.

With this build you have many ways to avoid bullets:

1. Sprinting with Stripped Down 
2. Critting to activate Empathic Evasion (as long as you're shooting or meleeing something, you're going to crit at least once a second)
3. Blocking with Deflector 
4. Sliding (especially effective with the extended duration that sprint speed buffs allow)
5. Dodging

I've played this build up to Auric, and it works there. I don't play Havoc, so no idea if it's good enough for that game mode.

Core rotation:

1. Activate Scrier's Gaze
2. Shoot enemies or engage them in melee (run at them with recon lasgun equipped if they're distant)
3. Use By Crack of Bone and/or Tranquility Through Slaughter to manage your peril as needed
4. Try to get elite/specialist kills to take advantage of Psykinetic's Aura's CDR while Scrier's Gaze is active
5. Spam Assail when peril is maxed out if you have good targets. Hordes, gunners, shooters, shotgunners, and ragers are the best targets, but it's decent vs anything not in carapace armor. Using your sword's warpshock slash here is also good if there's a cluster of enemies.
6. If you got some specialist/elite kills during Scrier's Gaze then it should be off cooldown or nearly there by the time the lingering effect is over.
7. Repeat

Special techniques:

1. Ranged fire immunity stacking - To get the full value out of being invulnerable to bullets you have to manage your various ways of doing so. You can be immune while sprinting due to Stripped Down, but the moment you stop sprinting, you can get gunned down if you haven't triggered Empathic Evasion from getting a crit. It's important to be always critting, running, sliding, dodging, or out of the line of fire. You're not permanently immune to bullets unless you're making sure to cover all the moments where you could be shot. Treat toughness as a small window of opportunity to get a crit or start sprinting/sliding if you start taking fire. You can use Deflector for a moment to catch your breath or figure out your next action.
2. Slide shooting - Get used to sliding around a lot and using your momentum and invulnerability to ranged fire while sliding to line up headshots with your recon lasgun or Assail. The amount of speed and momentum you have when stacking your movement buffs is ridiculous, so you can have extremely long (distance and duration) slides that give you ample time to line up a shot. Slide shooting is especially good for triggering Empathic Evasion while you're closing distance on a group of enemies so you're still immune to bullets while you start attacking them in melee. You can also activate both Mettle and Disrupt Destiny while slide shooting to reach your targets even faster.
3. Slide dagger throwing - Throwing out a dagger or two while sprint sliding at enemies is a great way to take out a few shooters, stack up the non-warp damage buff from Malefic Momentum, stagger a few gunners, and continue doing damage while sprinting at enemies. Throwing out even a single dagger while sprinting at a group of enemies lets you control the dagger while you're still running at them, potentially killing or staggering enemies, giving you time to get a crit with your sword to trigger Empathic Evasion.
4. Recon swap sliding - The recon lasgun has a very high sprint speed, which you can abuse to get high speed slides, even while in melee combat with nearly no sprint activation time. Swap to your lasgun, press the sprint and W keys, then nearly instantly hold down the slide key. You can swap back to your melee weapon once you're sliding or do some slide shooting. When done properly you can get a surprisingly high speed boost that will let you close gaps or dodge non-melee attacks, and you can even wind up a heavy attack while you're sliding at a new target or hold block to block melee attacks.
5. Melee sprint sliding - With the Covenant Mk VIII Blaze Force Greatsword you can activate sprint while winding up a heavy attack, which also means that you can chain that into a high speed slide while still holding your heavy attack. Melee sprint sliding is great for gap-closing to a new target or reaching your next Disrupt Destiny target.
6. Malefic Momentum upkeep - You can keep nearly 100% uptime on both Malefic Momentum buffs while in combat for a permanent +25% to all damage. The warpshock slash from the Covenant Mk VIII Blaze Force Greatsword can instantly max out the melee damage buff when thrown into hordes and Assail can be used to stack it up and for easy buff maintaining by just throwing a dagger out while in melee every once in a while. The warp damage buff is easy to stack by just meleeing enemies or shooting them, and even when you're spamming assail at the end of Scrier's Gaze you can still melee a single groaner or something to keep the warp damage buff up.
7. Tactical repositioning - Don't be afraid to run away from a pack of enemies if they're overwhelming you. You are the essence of SPEED when you've got your buffs up, so you can absolutely outrun whole packs of enemies if you maintain those buffs, and remember that you're immune to bullets while sprinting with above 50% stamina. Slide shooting can help you maintain your peril levels to keep your sprint speed from Scrier's Gaze up with Tranquility Through Slaughter while also triggering Mettle and Disrupt Destiny for more speed. Sliding will also let you conserve your stamina while regenerating a bit as well to stay above the Stripped Down 50% stamina threshold.
8. Push attacks - The push attack on the force GS is especially powerful, and has a medium range component to it. It will stagger or knock over any non-boss enemy that isn't being affected by stagger immunity, and is spammable as long as you have stamina and peril to spare. The only exception is that sprinting ragers sometimes won't be knocked over by the push attack, but they will once they start their combo attack.

Special/Elite management:

1. Bulwarks - A push attack or the fully charged warpshock slash will stagger bulwarks and open their shield for attacks as long as they're not being attacked by something else that's triggering their stagger immunity. Otherwise dodge-sliding around the side of their shield usually works.
2. Crushers - I prefer the Covenant Mk VIII Blaze Force Greatsword because you can push attack crushers to stagger them, then use the followup thrust attack to headshot and kill or nearly kill them (depending on your current buffs). Be aware of the stagger immunity CD of crushers though, as you can't consecutively stagger them with the force GS's push attack.
3. Ragers - Deal with them as normal, or when at least 2 of your sprint speed buffs are active you can straight up outrun ragers, especially when they slow down to do their combo attacks. You can use this to retreat and burn them down with your recon lasgun or just to reposition and then take them down with heavy attacks or push attack followups from your GS.
4. Flamers - Dodge to the side if they're targeting you, equip your recon lasgun, then just run up to them and melee them. Alternatively, just burn them down with ranged fire or Assail.
5. Bombers - These guys, especially tox bombers, can sneak up on you if you're not paying attention and kill you through sheer area denial if you're not aware. Be careful of getting yourself trapped by flames/gas and remember that you have SPEED on your side to reach them, outrun gas, or reposition before you get bombed to death.
6. Snipers - Laugh in their faces as they can do nothing to you while you just sprint at them and kill them in melee or slide shoot them.
7. Gunners - Sprint at them, slide shoot them to activate Empathic Evasion, and then melee them. Alternatively, suppress/kill them with your recon lasgun. If it's a whole pack of them, just passing your fire over the whole crowd at head height will suppress & stagger them while stacking up Infernus to kill them with burn DoTs.
8. Maulers - Heavy attack their heads (1 - 2 shots them depending on your current buffs) or if you've got a whole pack of them you can push attack a few of them to make space, and then use the followup thrust to oneshot headshot 1 of them (assuming you have at least some buffs up).
9. Shotgunners - See Gunners
10. Plasma Gunners - See Gunners, except that since they have carapace helmets I recommend shooting them in the body if you want to kill them with direct damage, otherwise let the burn from Infernus kill them if you're going for headshots.
11. Reapers - Mostly the same as gunners, but they're not as easily suppressed unless you get sustained headshots on them. I prefer to stack up Infernus on them while slide shooting them and then engage them in melee to kill them. I suggest hearty use of push attacks on their faces to stagger them for the push attack followup thrust. Otherwise they'll just keep shooting at you, and if you don't activate Empathic Evasion quickly you'll get gunned down fast.
12. Everything else - Nothing special for the other elites/specials, just use the advantages this build offers to kill them. Be aware that immunity to bullets does not mean immunity to nets.

Variants:

• MK VI greatsword: personal preference. I like having the stab after the push attack, but either sword mark will work
• Other recon lasguns: I'm sure the build works with other marks, but I think the torrent mark works the best with crits and infernus, especially being able to headshot a special for half a second and use True Aim to guarantee a crit, which with crit chaining will usually max out infernus stacks. Any man-sized enemy besides a crusher, rager, mutie, or mauler will die to the 12 burn stacks.
• Riposte could be swapped out with Shred or something else, but I'm always dodging with this build, so riposte is super easy to keep up.
• Infernus can be replaced with something else like Dumdum or Deathspitter if you want more direct damage instead of the burn damage, but I like infernus for its ability to do simultaneous damage to whole crowds of enemies by just spamming it on the heads of whole packs of specials/elites to stack instant 12 burn stacks on multiple targets.
• Swapping Lingering Influence for Perfectionism and Cruel Fortune synergizes with this build and will make you do more headshot/crit damage, which is what you're already aiming for, but I find it's less consistent to upkeep, and I just straight up don't have the talent points to afford it.
• Kinetic Deflection is great, but I don't have the spare points for it, and I find everything else in the build to be essential or more useful than KD.
• You can drop Warp Speed , but I think it's a much better build with it and it helps you outflank lines of gunners to engage them in melee. Also when combining it with the other speed boosts in this build you can actually outrun melee attacks sometimes, especially ragers while they're in a combo attack string.
• Battle Meditation is great and helps you stay in Scrier's Gaze longer, but I just don't have the points to afford it.
• Seer's Presence works fine with this build, I just prefer the crit from Prescience