Schmovement Crit Psyker
 Psyker Build - Warhammer 40k: Darktide 

This build focuses on maxing your critical damage and critical chance. With this build, you can consistently get to around 30-40% crit chance, depending on how comfortable you are on dancing around 80 Peril. With the Surge staff hitting multiple times per cast on a target, you're guaranteed to do massive damage. You will be able to consistently kill a Crusher in 3.5 full lightning casts. The key to this build is swapping between your weaponry freely and rapidly. 

Your surge staff will be used to clear medium to close range targets, primarily targeting specials and ranged attackers hiding near cover. Assail is inconsistent with finding targets behind cover, as they can hit terrain and stop. Spam your lightning without charging to amp up your crit damage via Perfect Timing. Lightning spam can also be used on smaller groups of enemies to clear and stun. 

Assail should be used to thin incoming hordes, or snipe far away targets like snipers and gunners. Activating Scriers Gaze will clear your warp charges, but the increased damage also allows you to insta kill snipers with an aimed Assail. Swapping to assail to quickly toss some charges down range now and again is also a good idea, as it can easily clean up spare mobs that would otherwise be a pain to single out each one. 

The MKV Warp Sword is your lynchpin for surviving hordes. Dodging and swinging in a circle strafing pattern lets you mop up nearly any size horde quickly. Make use of the charge function of the sword often, as it increases the power of every stat (including cleave), which makes it effective for buying some breathing room and slaying a good chunk of enemies in one go. Swapping to this weapon often and getting kills without its charge is also important to earn up to 20% extra damage across all of your weapons, further increasing the need to alternate between weapons rapidly. Activating Scriers gaze and diving headfirst into a horde makes quick work of most things. Be mindful of Ragers, as your blade will not stagger unless charged. 

Side note, if you haven't already, rebind your dodge key to spacebar, and jump to left alt. Having a bigger and easier to press button to dodge makes this build (and many others) far more consistent and less likely to die.

If you're skillful enough to maintain your buffs, you'll be doing 65% more damage baseline, have a 40% crit chance, and do 25% extra crit damage. And as your crit damage is based on your base damage, you can imagine where this goes.