PsyPurg
 Psyker Build - Warhammer 40k: Darktide 

To scratch the burning itch you get when you play psyker

Deimos Force Sword (or Duelling Sword IV/V) Most important part are these weapons get Uncanny which will let your Soulburn do full damage to Carapace armor. 
Perks: 

• Elite - Crushers are the primary enemies you will want to kill using Uncanny - this will increase Soulburn damage while you stack Uncanny. Elite lets you still one shot heavy special Maulers and Light special Ragers while increasing Crusher damage. Carapace/Flak are a fine options.
• Maniac - Necessary for the one shot Heavy2 head shot on Mutants.

Blessings:

• Uncanny - After stacking soulburn on all the crushers, swap to melee to get your uncanny stacks and watch them burn.
• Unstable Power - (or Slaughterer) It is easy to stack peril using Assail, and this lets you one shot head shot Mutants easier without having to get a kill. Shred is a great option, particularly with Mettle

Purgatus - Primary tool for dealing with hordes, elites and anything else from close to medium range.

Perks:

• Unyielding - Boss damage, a key part of the Purgatus staff identity. Also helps with your random Ogryn elite.
• Maniac - helps to kill Flamers, trappers, and Dreg Ragers in mixed hordes and do some extra damage to Mutants.  

Blessing:

• Warp Nexus - Crits apply 2 stacks of SoulBurn instead of one, maximizing efficiency.
• Blaze Away - More damage on hit, and for your burning affects, easy slot in.

Psyker has a base of 7.5% crit now, with Prescience and 5% crit node, you are at 16.5% base, and Warp Nexus with up to another 20% means you will crit very often for Mettle and Perfect Timing.  

WildFire is very lackluster right now  (if you don't believe me, go the the Psykhanium burn 20~ units to death and watch how little it spreads to adjacent units) Can only give 4 stacks, and can't go above what the initial unit had, so you normally don't see it spreading anything higher than 3-4~ which doesn't do a lot of damage. Easy pass for Assail which gives you access to med-long ranged damage to take out gunners/shooters. 

Venting Shriek is incredibly strong, and can easily increase the number of stack you have on an enemy by 6. Purgatus staff builds peril very slowly so we are running Assail so we always have a reliable and fast option for peril building. A single elite with Perilous Combustions kill will give 3 soulburn, trigger your ult for another 6 and it will reliably kill most ranged elites and specials. Make sure to hit 85% peril before triggering for 6 stacks.

Essence Harvest will give fantastic value as you will be getting charges from Assail killing Elites, and Soulblaze killing anything. Purgatus staff already has incredible Peril to Damage efficiency, so unless you have a staff with REALLY low Warp resistance I wouldn't bother with Inner Tranquility particularly since we will be dumping all warp charges per use of our ult, which will happen every 15~ seconds.  Warp Battery for is very optional - we rarely hit 6 stacks, let alone stay there when ult spamming.

Psychic Vampire is better when working with your team, In Fire Reborn is better when trying to solo/clutch, both are great options in this build, I find Psychic Vampire to be a bit more consistent.

Kinetic Deflection is a great option for clutch revives, kiting monsters, and if you run Deflector on your force sword