My Jack of all trades Psyker build (recent)
 Psyker Build - Warhammer 40k: Darktide 

I. Background

Just a build I've slowly developed while learning to play Psyker as my first character in the game. To an extent it defined its design - as I didn't want to be limited to a certain playstyle, and wanted to be able to perform well in random groups. It certainly lacks both utility and damage output, comparing to more "meta", specialized builds - but I still like to play it a lot, and was feeling myself well in pugs up to low level Havoc with it (if you bring Telekine Dome with you and use it properly, you're already half-redeemed lol).

II. General design principles

1. Has access to Brain Burst supported by Empowered Psionics - so you can deliver some heavy punch from a safe distance in a boss fight, or while helping with dispatching specialists and heavier mobs others don't have time to handle
2. Brings tons of utility with full Telekine Dome branch - both protection from ranged attacks and toughness regen to whole squad inside it
3. Additional toughness regen comes from crits (Mettle), melee attacks and kills (Warp Expenditure) and kills with warp attacks (Soulstealer) - the later includes the sword's discharge burst
4. Kinetic Deflection increases your versatility greatly, making your blocks much more reliable and allowing to pick up fallen comrades in a midst of a hoard (as you are considered blocking when reviving or rescuing allies)
5. Battle Meditation talent isn't taken to prevent Peril from decreasing too fast when a lot of chaff gets killed - as this build relies on its high level during melee fights to make most of One with the Warp, Warp Rider and Warp Splitting talents (and from Perfect Timing, which is triggered more often with more targets hit due to higher cleave) - as well as from Unstable Power bless on the sword
6. Anticipation is chosen over Immaterial Focus and Empathic Evasion for the sake of an extra dodge what is useful when wielding Force Greatswords, and BB while being attacked; both those options are still perfectly valid, with IF granting you stun immunity, and EV additional protection from range attacks

III. Choice of gear

With this build, I use Greatsword for most of the time during a mission, as it's pretty good at cleaving low-armored hoards. The crit blessing on it allows for extra damage and extra toughness regen (due to Mettle), while boosted cleave both from the Unstable Power blessing and Warp Splitting talent ensures you'll have enough opportunities to deliver the damage to as many targets as possible and "harvest" those crits, while fighting the chaffers. I prefer Mk.VIII for its versatility, it's easy to use when cleaving due to its wide light attack - while still allowing for extra damage and penetration with overhead hits provided by its heavy attack (so easy to target heads) and a precise powerful stab available as block's 2nd follow-up attack. The 1st block's follow-up attack staggers and drops to ground even Crushers and is a poor-man substitution for the lack of CC abilities on this build. I don't use bullet-blocking blessing with it as Telekine Dome usually handless the ranged threats good enough.

Shredder Autopistol with Strength increase blessings is used as a sidearm to quickly dispatch lone specialists and "softer" elites at close or medium range. I prefer it due to its ease of use, convenient and rather accurate braced mode of fire and high rate of fire that guarantees it will grow its stacks pretty quick and becomes rather good at staggering even the things that it can't kill when fired at a mixed hoard. Dumping a full clip in there often happens to be very effective. I don't use staves with this build - I think they don't synergize well with it, as they on their own increase Peril rapidly, and thus are much trickier to use during an intense fight when you are already at high Peril and need to use your ranged weapon urgently. Besides personal preferences, Bolt Pistol and Heavy Laspistol would probably be better as they offer significantly more punch vs heavier foes and bosses.

Weapons' traits are set to Maniacs and Flak Armored to facilitate dispatching of "softer" part of a hoard - heavier/armored foes more often will be dealt with using Brain Burst, or handled by teammates.

For Curios I go with full +Toughness line, as Warp Ghost already provides you +2 Toughness. Another good options is one +HP and two +Toughness, what helps any heavily-melee build. The two Revive Speed perks can be swapped for +Toughness ones if extra survivability is more important, but original variant synergize very well with Kinetic Deflection. I don't use much of damage resists in there, as Maniacs and Hounds are usually easy to avoid, or your teammates can kill them if you're disabled - and ranged threats are mitigated by the Dome. For that reason I felt it's worth to squeeze into a full stack of Ability CD reduction perk in here, which, after stacking with Seer's Presence, reduces Dome's CD by about 10s, further improved by Psykinetic's Aura.

IV. How it's played

This isn't a heavy-hitting, damage-focused psyker build, so don't expect to shine in melee with it. It hits hard enough to shred through the "softer" part of a hoard - but anything with armor may require additional effort, or falling back and using Brain Burst instead. 

If you face a wave with Peril too low, try to open the fight with 2-3 discharges from the sword. It won't do much damage except for the chaffers in the closest proximity - but it grows Peril rather quick, increasing your damage, cleave and toughness damage resistance via talents' synergy. Then proceed to spamming light attack chains to cleave the chaffers, while staying alive through dodging and blocking attacks. Use the block's follow up attack to push around dangerous foes like Ragers, Poxbursters or Hounds and use the stab attack or light/heavy attacks to finish them if possible. Kinetic Deflection talent  and the block's follow up (if it hits a foe) also help with keeping Peril high, to some extent.

Keep using the discharge attack from time to time to maintain your Peril in the red zone, until the hoard is thinned. Its damage is crap until at least one of two scales is filled - and they are reset on discharge. Now, with the new Warp Ghost talent, sword's alt attack needn't to be used as often as before to keep Peril up, helping with keeping its charge for a proper mass-murder; the charged attack cleaves weaker hoarders really well, and while at it replenishes your toughness via Soulstealer talent. Switch to the Autopistol or Brain Burst as needed, to dispatch priority or armored/beefy targets. As Crystalline Will talent isn't included, you have to be very careful with your Peril management in the heat of the fight.

Telekine Dome is useful even when not under ranged fire as it helps with toughness regen to the whole squad (and for you personally it's the only way of fully-passive toughness regen in battle) - so set it at spots where your group has to face a long fight with a wave right away and renew on CD until fight ends; another good move is to secure a spot when advancing into a new room full of ranged enemies. Keep in mind it has a limited durability, so, if possible, set it in more discreet places preventing focused enemy fire from all over the room. Due to Kinetic Resonance, setting it speeds up your Brain Burst's charging greatly, so your usual approach to Boss fights will be hitting them with the Burst 1-3 times until Empowered Psionics's charges are depleted, then dropping the Dome so you could keep charging your blitz rapidly.

Kinetic Deflection combined with +24% revive speed from curios perks allow you to pick up and rescue your allies against overwhelming odds, even if you need to first sprint to them, burning your stamina - as long as you have some room for your Peril to grow. Don't forget that the moment you've done assisting somebody you are no longer considered blocking automatically, so block or dodge immediately, or risk getting downed yourself. 

That's it, have fun!