Specialized for Elite Resistance Modifier
 Psyker Build - Warhammer 40k: Darktide 

After 500 hours of Psyker play, this is the best build I could come up with for the new modifier, and has so far worked splendidly.

This build revolves around staying between 60-80 Peril and staggering key enemies, such as Crusher/Bulwark/Reaper/Flamer/Trapper, and maintaining perfect positioning by utilizing the Combat Knife heavy attack sprint. The +3 stamina curio as well as the feat Kinetic Deflection can be swapped if you don't utilize blocking very often, but I found the combination to be too strong to leave without. I don't need any block efficiency at all to block a Daemonhost/Plague Ogryn indefinitely. Indefinite Chaos Spawn tanking requires good dodge practice.

Alternative Feat Choices

You really need the on demand nature of Quietitude to survive the crazy ranged hordes in this game mode, so I wouldn't recommend changing your lvl 5 feat. I don't recommend any of the feats over Warp Unleashed. The damage bonus is very noticable in this mode. Being able to cast 2-3 more full charged bursts with Inner Tranquility from 0 Peril isn't super useful given the fact that you shouldn't ever be at 0 Peril. You might be able to cast more without quelling, but the charge>burst>quell to 75% rotation is all you need, even when surrounded. I think with this modifier, Cerebral Lacerations is a must. We no longer get the 2 brain burst breakpoint on Crushers with it, but even so. Many enemies can no longer be 1 shot by a brain burst, that +25% damage is going to help the DoT from bleed stacks or soulblaze finish them off for you. If you feel you don't block enough to make it worth taking or you have no intention of tanking Daemonhosts, you'll probably get much more use out of Kinetic Shield over Kinetic Deflection. I love Kinetic Flayer too much to not have it, but I can see reasonings for an extra 8% damage from 2 charges or the ability to maintain soulblaze without relying solely on the 1-in-5 crits. I hate losing warp charges, so I only ever run Kinetic Barrage. If you don't get much use out of the hastened Brain Bursting, either will work well. Quicken will help in tight situations more often and Ascending Blaze helps maintain soulblaze as well as give you access to “passive” warp charge generation.

Alternative Perks/Blessings/Melee

In most game modes, you just don't get enough value out of Burning Spirit for it to be meaningful, and I would recommend using Rending Shockwave instead if you only have 1 good Trauma staff. However, since Elite Resistance boosts enemy HP values quite a bit, I've found the added burn damage to be extremely helpful in managing hordes as well as those now enormous Reaper/Crusher health pools. Of the 2 Trauma staff perks, Flak is most important. Carapace just makes dealing with Crushers easier, but Flak+Manic is just as viable. Even ranged crit is a good one. Just don't keep unarmored/infested. Really anything else works.

If you don't like to use the Combat Knife or just prefer the force weapons, The Deimos is the better option of the 3 IMO. Typical setup, slaughter/deflection and flak/maniac. This gives you the ability to handle mutants on demand, a decently rolled Deimos with +25% vs Maniacs can 1 shot headshot them. Just takes some practice to get the head consistently.

Alternative Curio setups

I choose health curios over toughness almost 90% of the time. On paper, having more toughness should be better because its constantly being regenerated. In practice, I've found that my toughness is almost never broken due to melee attacks and thus I don't need a lot of toughness, I just need the ability to regen it on command.  

***If you are unaware, you get an 85% damage reduction bonus against ranged attacks whenever your toughness breaks by ranged attacks***

This essentially means that by using Quietitude's on-demand nature I get far more value out of my Toughness by treating it as a buffer for mistakesorpoorpositioning rather than a secondary health pool. Toughness breaks, I'm immediately dodge sliding to cover while quelling, giving me just enough toughness between enemy shots to break toughness and get that damage reduction again. Repeat until safe. Bringing 2 health curios also means that you still have 2 wounds in Grimoire runs! No corruption resistance required!

For perks, I'd say the only necessary one is damage resistance (gunners). The others are really personal preference. I like combat ability regen because it shaves off 3 seconds which doesn't seem like much, but I swear has saved my life on countless occasions. Good alternatives would be block or sprint efficiency (sprint only if using knife), more bonus health, or standard corruption resistance (why the fuck is this stat split between grimoiress and other forms of corruption????).