Support-leaning Smite/Dome Psyker
 Psyker Build - Warhammer 40k: Darktide 

I. Background

An attempt to capitalize on Psyker's support capabilities, just for the sake of it and doing things differently. The build focuses more on helping others than on killing stuff yourself - but still leaves an option for a strong melee and some range anti-armor/anti-specialists option via Bolt Pistol.

II. General design principles

1. Assumes Smite will only be used for a prolonged period to ramp up Peril when using sword's discharge attack isn't optimal to do that (when you don't want to lose its charge) - or when in need of urgent mass CC effect to let others save the day. Empowered Psionics make it better - and its Psychic Leeching sub-talent adds a support edge to Smite by allowing you to quickly restore up to 60% toughness to yourself and your teammates by tapping LMB 3 times
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) and kills with warp attacks (Soulstealer) - the later includes the sword's discharge burst
4. Kinetic Deflection increases you versatility greatly, making your blocks much more reliable and allowing you to pick up fallen comrades in a midst of a hoard (as you are considered blocking when reviving or rescuing allies)
5. Puppet Master talent is justified by synergizing well with Psykinetic's Aura and Psychic Leeching talents, enhancing build's support potential. If needed, two points spent on getting it could be moved to Quietude and Warp Expenditure, decreasing your support range, but increasing survivability passively
6. Battle Meditation talent is deliberately bypassed via Perilous Combustion 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
7. The build lacks when it comes to boss fights, making you almost fully rely on melee for it, what may require some adjustments for newer players

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 Unstable Power blessing coupled with Warp Splitting talent significantly ramps up its hoard clearing and single target damage capabilities as long as your Peril stays high - ensuring 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 even Crushers and is standard opening move in a fight with any strong melee opponent you meet.

Bolt Pistol is used to provide an option when dealing with armored foes and bosses - as well when as with specialists at range. For optimal performance it should always be fired while aiming down the sights (it's still possible to dodge around while at it). I wouldn'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.

Weapons' traits are set to Maniacs and Flak Armored on the sword to facilitate dispatching of "softer" part of a hoard, and the ones on the Pistol are geared towards extra damage to "heavier" foes (including bosses).

For Curios I prefer to use one with extra stamina, to compensate for psyker's low innate stamina pool and help him to move around quickly (a useful trait for a more supportish build). Revive Speed perks synergize very well with Kinetic Deflection. allowing you to sprint to a fallen comrade - then rescue them, ignoring the hoard. 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

The build can be pretty strong in melee, assuming you can both keep your Peril high, as well as swapping damage types between warp-based and non-warp (to benefit from Malefic Momentum talent) - while not wasting your sword's charging until it's reached at least the first threshold. Juggling between the three may first seem daunting - but it gets better with practice. The important part is to not focus on doing everything in most optimal way, until it will just start happening naturally. Better do some damage right now than waste time and take hits, trying to prepare for a future ideal attack.

If you face a wave with Peril too low, try to open the fight with 2-3 discharges from the sword or the Smite's discharge up to the limit. Though sword's discharges don't do much damage unless charged up to the threshold, they still stagger the hoard, giving you an upper hand - and grow 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. The block's follow up also grows Peril quickly if spammed (if it hits a foe), so can be used to keep it high too. Due to Kinetic Deflection blocking against a crowd now also allows you to grow Peril before hitting them back hard.

Keep using the discharge attack from time to time to maintain high level of Peril, until the hoard is thinned. Its damage is crap until at least one of two scales is filled - and they are reset on discharge. With big enough crowds though - or when finding a right way of juggling between Smite and melee - you'll have opportunity to do a "charged discharge" too - it cleaves weaker hoarders really well, and while at it replenishes your toughness via Soulstealer talent. Switch to the Bolt Pistol to get rid of specialists or deal with armored foes and bosses you don't want to approach - or to Smite when urgent mass CC is needed. 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.

By quickly activating Smite repeatedly (with LMB taps for example) you can burn your accumulated Empowered Psionics charges to restore up to 60% toughness to yourself and your mates in coherence in a few seconds, when needed. As you can replenish those charges pretty quick during your normal fighting loop, it may open a refreshing possibility of filling a role of combat healer for your psyker, if you'll find a way to use it efficiently.

Kinetic Deflection allows 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.  Revive Speed perks on Curios make you even more efficient at this (and those also speed up other types of assist, making it a good addition to your support toolset). 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!