Psyker Critical Warp Shock
 Psyker Build - Warhammer 40k: Darktide 

Overview:

This is a high-DPS build for the Psyker, using the the Electro staff's primary attack. Most of those attacks will be doubled by the Surge blessing due to the build's high crit rate. Scrier's Gaze with Warp Unbound allows you to continue spamming attacks for 10 seconds after reaching 100% peril, during which time you'll have the full bonus from Warp Nexus, and Warp Rider. Due to the high crit rate and attack rate, you'll also have high uptime with Empathic Evasion to automatically evade ranged attacks.
 

It's worth noting that this build requires good aim to reach its potential. You want to be aiming for weakspots whenever possible. Aiming center mass is generally fine too, especially at long range, but you'll do significantly more damage with weakspot hits against most targets.

I recommend the Tactical Axe for efficient horde clear and great critical rate to regen Toughness. The Mk VII is my favorite since it has a farther reach than the other Marks, but use whichever you like best. Despite not being a true "melee build," it still has Scrier's Gaze and Malefic Momentum and can perform better than the average Psyker build in melee combat.
 

Crit Calculations:

Minimum  staff crit chance: 7.5 (base) + 21 (staff 80% Crit Bonus) + 5 (staff perk) + 5 (Surge blessing) + 5 (Warp Nexus blessing) + 5 (Crit Chance Bonus node) = 48.5%
 

Maximum staff crit chance: 7.5 (base) + 21 (staff 80% Crit Bonus) + 5 (staff perk) + 5 (Surge blessing) + 20 (Warp Nexus blessing) + 5 (Crit Chance Bonus node) + 20 (Scrier's Gaze) = 83.5%

Minimum  axe crit chance: 7.5 (base) + 12 ( axe 80% Crit Bonus) + 5 (axe perk) + 4 (Shred blessing) + 5 (Crit Chance Bonus node) = 33.5%

Maximum axe crit chance: 7.5 (base) + 12 (axe 80% Crit Bonus) + 5 (axe perk) + 20 (Shred blessing) + 5 (Crit Chance Bonus node) + 20 (Scrier's Gaze) = 69.5%

Warp Damage Talents Testing on Crushers:

No Talents (Base Damage):

Head: 39/87

Chest: 14/66

Limbs: 7/33

Perfect Timing: ~+15%

Head: 41/100 (+2,+13) - Non-crit only ~+5% compared to other hits ~+15%

Chest: 16/76 (+2,+10) ~+15% on both

Limbs: 8/38 (+1,+5) ~+15% on both

Warp Rider: ~+19.3%

Head: 42-103 (+3,+16) +7.7% on non-crit, +18.4% on crit

Chest: 17-79 (+3,+13) ~+21% on non-crit, ~+19.7% on crit

Limbs: 9-40 (+2,+7) ~+28.6% on non-crit, ~+21.2% on crit

Malefic Momentum: ~23.3%

Head: 43-108 (+4,+21) ~10.3% on non-crit, ~24.1% on crit

Chest: 18-82 (+4,+16) ~+28.6% on non-crit, ~+24.2% on crit

Limbs: 9-41 (+2,+8) ~+28.6% on non-crit, ~+24.2% on crit

Empyric Shock: ~+31.9%

Head: 44-116 (+5,+29) ~+12.8% on non-crit, ~+33.3% on crit

Chest: 19-88 (+5,+22) ~+35.7% on non-crit, ~+33.3% on crit

Limbs: 10-44 (+3,+11) ~+42.9% on non-crit, ~33.3% on crit

Penetration of the Soul: ~+59% 

Head: 53-121 (+14,+34) ~+35.9% on non-crit, ~+39.1% on crit

Chest: 28-92 (+14,+26) ~+100% on non-crit, ~+39.4% on crit

Limbs: 14-46 (+7,+13) ~+100% on non-crit, ~+39.4% on crit

Electro staff primary attack deals roughly 2-4x damage on a crit, depending on enemy armor type, and even more on a critical weakspot hit. You can Inspect the staff in your inventory and View Attack Breakdowns to see the exact numbers. Its only notable weaknesses are carapace and unyielding armor types, but the secondary attack deals decent damage against those types, and Penertation of the Soul doubles the primary attack damage on carapace.
 

Gameplay:
 

Against hordes: melee (light attack -> heavy attack)
 

Against specialists/gunners: staff bolt

Against reapers: staff secondary attack
 

Against crushers: staff secondary attack
 

Against bulwarks: staff secondary attack

Against maulers: staff bolt

Against ragers: staff bolt
 

Against other elites: staff bolt
 

Against Beast of Nurgle: staff bolt (weakspot), or staff secondary attack
 

Against other monstrosities: staff bolt (weakspot), or staff secondary attack
 

If your peril starts to reach 80+% during Scrier's Gaze, you'll usually want to quell down to at least half to avoid reaching 100% and ending Gaze too early. You have overload protection from Warp Unbound for 10 seconds after reaching 100% peril during Gaze, but you lose the +20% crit chance upon reaching 100% peril and enter the "lingering" phase. Quelling also allows you to stay in Gaze longer and stack up the damage buff that continues during the lingering phase, providing up to +30% damage if you can go 30 seconds without reaching max peril. In practice you won't get the full 30% most of the time, but it's beneficial to extend the Gaze duration if you have time to quell during combat.

Skill Tree:

Due to the high crit rate and attack rate with the staff bolts and tac axe, Mettle handles the toughness recovery for the build.
 

Channeled Force might seem like they'd be perfect for this build, but in practice I think there are better places to spend points. CF requires you to full-charge a secondary attack every 5 seconds if you want the bonus, which is cumbersome and might even be a net DPS loss since your primary attack is better than the secondary against most targets.

Seer's Presence is generally the best aura for Psyker, and especially for this build since Prescience would cost an extra point. Higher uptime of Scrier's Gaze is more damage and more peril management. Empathic Evasion is the core defensive node of the build.
 

Scrier's Gaze is a huge force multiplier for this build and is recommended for Auric Maelstrom and below. Telekine Dome (aka "bubble" shield) is popular in Havoc missions and is probably the optimal pick there unless you already have a couple on the team. For Scrier's Gaze upgrades, Precognition is preferred for melee synergy, but Reality Anchor can make it easier to prolong Gaze for maximum benefit. Warp Unbound is obviously required to avoid constantly blowing yourself up, and also lets you get max value from the various peril-based buffs.
 

Warp Siphon not only can provide a nice damage bonus, as well as get Scrier's Gaze back up faster, but if done correctly on harder difficulties, potentially lead to an infinite Scrier's loop.

Warp Rider is a mainstay of high-peril builds and is especially good combined with Warp Unbound, this also works with PotS. Solidity for better quelling, which translates to less downtime during combat and better Scrier's Gaze uptime.