Hash-slinging slasher | Assail | Scrier's Gaze | Disrupt Destiny | Auric
 Psyker Build - Warhammer 40k: Darktide 

This is a high-damage build intended to be competent at doing just about anything at auric levels of difficulty.

Basics

• Horde clear: Use assail in conjunction with the sweeping attacks from the Mk VI blade to make short work of hordes.
• Average shooters/gunners: Use assail in conjunction with the "Empathetic Evasion" talent to slay heeps of ranged units while taking minimal/no damage.
• Ragers: Use assail or the revolver to dispatch ragers en masse. Use the knife's block + push attack to deal with ragers during windows of opportunity.
• Chargers: Best to use the knife to quickly take care of these big boys.
• Disablers: Everything in the build is capable of quickly slaying these these units, especially with headshots. Well, except for dogs, don't use assail on them as it's not the most effective at killing them.
• Carapace armored units and chaos ogryns: Aim for the head and use the revolver to dispatch these units quickly and safely, or use the knife to get up close and personal at your own peril.
• Bosses: Use the knife's bleed and crits to take down bosses. This is not the fastest method at taking down bosses relative to other boss-focused builds, but it's definitely no chump either.
• Mobility: Use the knife, "Disrupt Destiny", and "Scrier's Gaze" to quickly reposition when necessary. It helps if you view the blue-outlined enemies as brief speed-boost power-ups. You'll be a blur.
• Survivability: This build includes a lot of toughness damage reduction. Given "Scrier's Gaze" is active, then you'll have anywhere from 45% to 68% toughness damage reduction and a total toughness of 179 via the talents and curious. Use assail in conjunction with "Soulsteeler" and "Mettle" to quickly regain toughness in hordes.
• Damage: Most of your damage is going to come from critical hits, especially critical weakspot hits. Crits are made more frequent via "Scrier's Gaze" which also makes them more potent as well. "Disrupt Destiny" also further increases the potency of critical/weakspot hits.

Tips & tricks

• You'll want to frequently switch between slinging out assails, poking eyes with the knife, and popping heads with the revolver. This switch between assail and conventional weapons allows you take advantage of the "Malefic Momentum" talent which further increases your damage.
• Use the knife's movement boost to reposition when things get dicey, picking up a quick blue-outlined-enemy-kill along the way for an added speed boost if you can. 
• You can rapidly light-attack/push-attack with the knife to get ranged-attack immunity with crits if meleeing while being gunned down e.g. if you're close to a gunner ogryn, you can spam melee attacks at it while it's shooting you and it won't really do any damage to you. 
• Use "Scrier's Gaze" whenever there's combat and it's up, which, in auric, is almost all of the time. The cooldown reduction via "Seer's Presence" and the curios helps shave some vital seconds off of its cooldown. This ability is a massive boost to your survivability and damage. "Warp Unbound" allows you to take full, care-free advantage of the "Warp Rider" perk to toss out +20% damage assails at 100% peril. Don't worry too much about quelling peril to maximize its uptime, just pop it, and start killing.
• Do not use assail for pox bursters as the shards can knock them towards the team.

Flexibility

There are two toughness nodes that can be swapped for other talents. Given 1-2 free points, some suggestions are:

• "Perfect Timing" to further boost assail damage
• "Kinetic Presence" for added elite unit damage
• "Anticipation" for even better dodging
• "By Crack of Bone" if you really want to lean on the knife and extend the duration of "Scrier's Gaze"

I personally just prefer the +30 toughness over the other options in the tree.