Electro Shriek! Big Damage! Psyker's squishy? Just DELETE Everything!
 Psyker Build - Warhammer 40k: Darktide 

Build Brief:

This build utilizes the auto-aim nature of charged Nomanus Mk VI Electrokinetic Force Staff and the mass soulblaze damage over time from Venting Shriek Creeping Flames (sets whatever medium range on your screen on soulblaze, including enemies behind walls). When the player is forced into melee, Covenant Mk VIII Blaze Force Greatsword with Peril Equilibrium will allow Venting Shriek to be available. 

There are alternative builds at the bottom of this guide.

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Depths of the Damned Patch:

Previously, this Psyker build had few alternatives to go for. Now, there is 1 additional free point (allocated at Anticipation) in addition to the core build.

DPS is shifted into more player damage from melee/staff/Kinetic Flayer because of Psykinetic Grip Focused Warp Peril Equilibrium; but lowered from Perilous Combustion nerf of 3 to 2 and Psykinetic's Aura being player only trigger instead of allies inclusive. Venting Shriek is less readily available. 

My thoughts?
Before patch, I felt like electro staff could use a bit more damage for havoc 40s. Now it has it in addition to Peril Equilibrium. I like it overall. 

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The Main Damage:

Nomanus Mk VI Electrokinetic Force Staff 
Use Flak Armoured and Unyielding Perks, with Warp Flurry and Warp Nexus.
Flak Armoured allows you to kill most elites at 2 half charges, and Unyielding will allow you to eat through monstrosities.

The gameplay is simple, half charge almost everything. This allows you to trigger Kinetic Flayer faster than waiting for a full charge. There is not much difference in DPS between full charge and half charge. I'd generally recommend full charging monstrosities/bosses, and half charging everything else. Be aware that Poxburster may jump in strange directions because the electric staff chain lightning can push it towards you, rather than away from you (if you target an enemy behind the burster instead). Kinetic Flayer will also NOT trigger on Poxburster.

Once you're above 85% peril (threshold for 6 stacks of Creeping Flames), turn to face the thickest of hordes or monster, and use Venting Shriek. The soulblaze from this can normally delete most hordes on your screen and the DoT damage is surprisingly decent on Monstrosities. You can run in circles kiting 2 full hp plague ogryns while targeting trash/elites with staff and venting on the ogryns; the plague ogryns will die after a minute or 2. 

Why Soulblaze? 
While exact soulblaze damage varies per enemy, think of it like this:
1 Stack: Single digit damage ticks.
3 Stacks: Around 15 damage ticks.
6 Stacks: Around 60-140 damage ticks.
9 Stacks: Around 90-300 damage ticks.
12 Stacks: Around 120-400 damage ticks.
15 Stacks: By the time this non-boss enemy reaches this many stacks, it's probably almost dead.

Kinetic Flayer (triggered by any damage including soulblaze) instant kills an elite, spreading Perilous Combustion. Venting Shriek Creeping Flames spreads 6 more stacks. Any additional elites/specialists killed spreads more Perilous Combustion, and elites/specials dying from soulblaze triggers more Perilous Combustion. It's a runaway soulblaze effect. The more grouped up elites/specialists are, the higher your output.

Please know, soulblaze spread from Perilous Combustion and Venting Shriek does NOT spread on unaggroed Demonhost (patch 7 Oct 2025).

When killing Monstrosities, your main priority is to kill elites near the monster to stack soulblaze. Also note, when playing with teammates, pay attention to what type of enemies are nearby. You are predominantly ranged, so you can easily turn to remove elites and specialists that are coming to disrupt your team from killing the monster. When killing Captain bosses (the human bosses with bubble shields), the staff damage is noticeably lower, switch to Melee and heavy attack the boss only when you deem it safe to do so (melee deals double damage to the bubble). 

Without Empathic Evasion you'll need to continuously Line of Sight enemies (hide behind boxes/walls and take enemies one at a time). 

Please know, you can SLIDE + RELOAD to keep mobility up. You can also SLIDE + HALF CHARGE turn 180 to hit enemies behind you as well. You will NEVER need Mind in Motion because of this.

Also note, the staff is an aimbot weapon, on the video (outdated but shows general gameplay), you'll find that I'm swinging my screen zapping at nothing. This is because I'm sweeping to see if it connects to anything.

If something is incredibly far away, use staff light attacks or Brain Rupture.

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Melee:

How to melee?
If you need to swap to melee because you're being cornered, the first thing you should do is push. Staggering the mobs in front of you would set you up to not being hit, and keep holding block to stop stray attacks if the push doesn't stop additional mobs/elites. Only after that, should you start attacking. If you're trying to get out of a situation, spamming push is an option too. Once you build this habit, you'll begin to understand what pushing does per enemy type, and then you can adjust your gameplay accordingly to your experience. When you have 75% Peril from Peril Equilibrium, feel free to use Venting Shriek.

Covenant Mk VIII Blaze Force Greatsword Most player friendly:
I have selected this for simple horde clearing with Infested/Unarmoured perks, with Shred Wrath blessings. It is definitely overkill for Auric Maelstroms, but in higher havocs, hordes can take a while to kill when you're cornered. If you feel like you're taking chip damage too much while using Greatsword, use Momentum Wrath instead. Cutting through hordes will charge up the greatsword special attack quickly, don't forget to use it (wipes most of hordes with it, passes through objects).

Cadia Mk XIIIg Assault Chainsword Different flavour, still friendly:
With the Chainsword buffs, if you enjoy spamming light attacks to take care of hordes (like me; which is not good, best to push enemies too), then with Infested/Unarmoured perks and Shred Wrath, this will clean up hordes faster than the Greatsword due to faster attack speed and higher base light attack damage (150+ on Greatsword, 210+ on Chainsword). However, Greatsword has a wider sweep area, making greatsword the safer pick. Enemies can hit you easier because of Chainsword's smaller sweep attacks. Please don't forget to use Special Action heavy attacks on captain shields, it cuts through those quicker than left click spam.

If you're bored of Greatsword, give Chainsword a try. It's fun and allows you to move slightly faster.

Catachan Mk VI Combat Blade Needs a bit of experience to run around and reposition:
Slot in any Perks with Riposte Precognition, this is mainly used as a mobility weapon to get in and out of situations. Alternate light attacks and push for hordes, otherwise hold heavy attack while sprinting to run away faster. 

Maccabian Mk IV Duelling Sword Decent heavy attack damage, high mobility, needs experience:
With Unyielding and Carapace Armoured Perks, Thrust Riposte for Blessings; this is generally a go to weapon for an all rounded Psyker. Light attacks and push for hording, heavy attack heads/weakspots on everything else.

Deimos Mk IV Blaze Force Sword The one melee weapon that does everything?
If you want to master 1 weapon that does everything and never want to swap to any other melee, this is it. Warp Resistance 60%, Crit Chance and any damage perk, Blazing Spirit Uncanny Strike. Boss damage? Soulblaze. Crusher? Uncanny. Stagger? Heavy attack. Go to Psykhanium and try it out. You'll see what I mean. The single target DPS on this weapon is higher than the weapons mentioned above.

As a side note, I use all weapons mentioned depending on mood. 

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Curio:

I default to Cooldown Reduction, the other 2 perks are optional. Note that stamina regen, block efficiency, and faster revives are great options.

I would aim to get Curios that suit your play style. If you have absolutely no idea what to do with Curios, grab Health, Toughness and Cooldown Reduction; and then adjust to get what you need depending on what you're struggling with. The stamina curio is up to you as well; sometimes, I find myself with no stamina to push a poxburster or that I don't have enough stamina to block multiple attacks (reviving someone for example), hence why I went for that instead to match my needs. 

Just a rule of thumb, you don't need a ridiculous amount of toughness, minmax build crafters will tell you that Health is more important than Toughness due to the mechanics of being hit while not on maximum toughness (if you get hit while not at max toughness, the damage is spilled onto hp, that is, you survive longer for more hits with higher hp in general). If you continuously get hit twice then recover toughness to max, the second hit will always chip away your hp, a very high maximum toughness in this case would not matter. High toughness does allow you to take a 3rd or 4th hit better, as the toughness reduces hp damage taken so long as you have toughness. If you run out of toughness, it's all going to hp damage direct. But remember, you have a lot of toughness regeneration/damage reduction talents to make up for this, I don't know what the optimal hp vs toughness ratio is for the best durability; because I think it depends on how often you get hit consecutively.

What is used in the video is Health + Toughness + Stamina Curios, with Toughness/Health/Cooldown Reduction perks on all. I believe this provides the best balance for all situations. 
 

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Talents:

Survivability: Quietude Mettle Souldrinker is generally more than enough to keep your toughness up. The idea is to recover chip damage. Unfortunately, Psyker does not have the luxury of tanking hits. Psyker has 2 states; you recover chip damage and move on, or you take too much damage too fast and is dead; no amount of toughness regen will save you from fast damage taken. Why Quietude and not Soulstealer? Sometimes, there are moments where there is a boss or monster, and there is no other enemy at all. Soulstealer would be useless in this situation, whereas Quietude will be useful in all situations.

Just a Dream and Immaterial Focus are interchangeable. Either way, taking damage is just no no as Psyker. Hence, Anticipation will help you dodge for 0 damage taken.

Do note that Empyric Resolve allows you to spam staff longer before needing to reload. Without this, the staff feels like a peril hog.

If you want Kinetic Deflection, I would remove Anticipation. If you're new to psyker and you're asking "why would I want that?" it's because you can block anything without the cost of stamina. This means you can revive players and block attacks at the cost of peril. You can also hold block on a demonhost while in a corner, venting, and your team has a non running around demonhost to full dps on. It is true that you shouldn't wake a demonhost to begin with, but with the chain lightning from Nomanus Mk VI Electrokinetic Force Staff, mistakes happen, and it's nice to be able to hold it without worry.

What makes Peril Equilibrium so good?
The soulblaze from Creeping Flames triggers Kinetic Flayer, triggering Perilous Combustion.

Perilous Combustion Wildfire are bread and butter for the electric staff because of the nature of being able to remove elites quickly. There are clutch moments where the soulblaze killed enough enemies in the way for me to escape a cornered situation.

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Alternative Playstyles:

The alternatives do not change the overall impact of this build. They are more variances of playstyles.
 

More Charge Damage:

This is great for people that don't mind adding a light attack every 5s. Remove Immaterial Focus Anticipation for Just a Dream Channeled Force. You'll get +10% to charge damage. Simple and effective.
 

More Overall Damage:

This is for people that don't camp staff permanently, and adds a level of comfort because of the higher melee output (things die a bit faster when you're cornered). Swap Peril Equilibrium or Psykinetic Grip for Malefic Momentum. This adds +25% to your melee, and +25% to staff/soulblaze/greatsword special attack for 10s after 5 horde melee kills. I suspect that this would outpace this build guide's damage when played optimally; but it does require an active upkeep of the buffs. 

On Skitarii, there are talents like Hybrid Combat Covenant that decay 1 stack at a time. I pray that the devs make this decay 1 at a time too. If they do this, then this will become staple to the build.
 

Machine Gun Psyker:

You like guns blazing Veteran but don't like ammo management? Remove Anticipation Immaterial Focus Peril Equilibrium for Just a Dream Channeled Force Empyric Shock. This drastically changes the playstyle away from charged attacks as a main. The maximum effect of this set up is +50% to light attacks, and +10% to charged. For the staff, swap Warp Flurry for Surge. To play this, you full charge once every 5 seconds, and light attack spam the rest of the time. You'll need to aim for weakspots to maximize damage. 

You might think, why not use Equinox Mk IV Voidstrike Force Staff instead? It's because Nomanus Mk VI Electrokinetic Force Staff has higher inherit crit chance. Surge will trigger more often with electro staff than strike staff.
 

No Melee:

If you're not comfortable with melee, then swap Peril Equilibrium out for Essence Harvest, Just a Dream or Empathic Evasion. Essence Harvest allows you to have toughness regen consistently, Just a Dream will make you as tanky as Psyker can get (still squishy though), and Empathic Evasion will help you dodge ranged enemies on crit (staff crits often). 

For new players (up to Auric), I recommend Essence Harvest. For below 25 Havocs (and Auric Maelstrom), I recommend Just a Dream. For higher Havocs, I recommend Empathic Evasion.
 

Full Defense:

This is great for players who are learning Psyker and want the most forgiveness possible. Swap out Peril Equilibrium Psykinetic Grip Penetration of the Soul for Just a Dream Empathic Evasion Essence Harvest. Psyker is STILL squishy even with these talents, but it should help new players stay alive longer to learn from mistakes.

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Mods?
I understand that modding Darktide is not everyone's preference. To aid playing this build specifically, these are mods I recommend that can be found on Nexus Mods. Know that adding mods to Darktide will make the game easier (explained below). Please use mods under your own discretion. I don't hold any responsibility on whether your game becomes unstable or not. 

Skitarius = You can bind a single button to do any repeating action, and it also stops you from overloading while holding down that button. When I hold my mouse 5 button, staff is charged at 50% and casted, holding this button repeats the action until I reach critical peril, and will not overload.

Peril FX = I reduced the volume of critical peril down to 33%, allowing me to hear enemy movements better.

Healthbars = Allows me to see elite/specialist hp, so that I can specifically target low hp enemies to kill them for Perilous Combustion.

Without these mods, I will overload often (Skitarius), will get caught more often (Peril FX), and will not deal as much damage (Healthbars). While I have completed Havoc 40s, I do not claim to be skilled when I rely on mods that make the game easier for me.

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Btw Smite and that new shotgun on psyker is busted...
The video attached is outdated but still useful to see how it plays, I may update it someday....................
Thank you Platzetta for crediting me on their build guide. I don't wish to claim this build as "mine" since anyone can come up with it, yes I still play Darktide.