An eye for crits (Assail - Scryer's Gaze - Warp Siphon)
 Psyker Build - Warhammer 40k: Darktide 

I'm a psyker but... *cocks gun*

This is a straightforward Scryer's Gaze crit build.

Maccabian Mk IV Duelling Sword is a powerhouse of a melee weapon, able to handle almost everything well while providing a lot of mobility. The crit bonus goes well with finesse, and several nodes of our talent tree benefit from crits. Thrust speeds up our boss & armored kills.

The +2 Stamina makes up for our lack of +3 stamina curio, which makes room for another toughness curio (important because this build spends a lot of time on the frontline).

Bolt pistol with Surgical & Deadly Accurate means a whole lotta damage. The quick swap means specials can be handled well, and the stagger AoE can buy us precious time when facing gunners.

Alternative: Agripinaa Mk XIV Quickdraw Stub Revolver, with Crucian Roulette & Hand-Cannon / the Zarona one with Surgical & Hand-Cannon.

Assail helps us deal with pesky gunners, or to thin a horde before engaging it. We don't take Ethereal Shards because we have Warp Splitting, meaning that at medium - high peril anything we throw pierces many targets, including our Assail shards. Assail also helps us maintaining a medium peril inbetween two Gazes.

Warp Unbound gives us the ability to use Assail even after reaching max peril due to Scryer's Gaze, meaning if a squad of gunners shows up right as we're at 100% peril, we can still throw a few shards without suffering perils of the warp.

Warp Siphon shortens our time between two Gazes, and Essence Harvest patches somewhat our frailty.

Weapon alternatives (without order): 

Melee:

-Illisi Blaze Force sword (Deflector, Precognition). Force swords have the advantage of providing defense against gunners (our nemesis as psyker), and Precognition boosts our crit and weakspot damage. I prefer the Illisi because the special attack doesn't lock you in place.

Ranged: 

- Graia Mk VII Vigilant Autogun (Surgical, Deadly Accurate) better against scattered groups of gunners, worse against carapace.

- Agripinaa Mk XIV Quickdraw Stub Revolver (Crucian Roulette, Hand-Cannon) better burst damage in a pinch and against specialists due to penetrating shots, worse against groups of gunners.

- Accatran Mk XII Recon Lasgun (Headhunter, Infernus) better dps overall & no need to aim well, worse crowd control and against carapace