Greatsword Berserker Psyker
 Psyker Build - Warhammer 40k: Darktide 

This build basically plays like a Zealot, staying in melee 90% of the time and just using the ranged weapon for picking off specialists/gunners and for monstrosity DPS. Force greatsword is a joy to use and works well against all enemy types. There are several good options for the 2nd blessing: Precognition, Shred, Wrath , or even Deflector. Unstable Power has pretty good uptime with Scrier's Gaze+ Warp Ghost, even with the frequent quelling from By Crack of Bone, so I prefer it in this build. Damage vs flak perk doesn't seem to change any important breakpoints at least on Auric difficulty, so I went with damage vs carapace and unyielding.

Bolt pistol works really well in this build for a few reasons. It's very fast to pulling out and snipe a specialist while already engaged in melee, it has good DPS against reapers and bosses/monstrosities, and it can trigger Kinetic Flayer with both the AoE explosion and the bleeding ticks from Puncture. Since it can kill most targets in 1-2 shots, it's pretty ammo efficient too. The 2nd blessing can be swapped to Lethal Proximity if you want, but I like Run 'n' Gun because it improves the weapon's accuracy. Bolt pistol only loses ~5% reload speed by dumping that stat, so I think that's the best option; 80% Mobility and Collateral both have more tangible benefits.

Scrier's Gaze already has a very short cooldown, so I don't think Seer's Presence aura or ability cooldown curio perks are needed. Seer's Presence is still useful to teammates, but crit builds are common enough these days that Prescience also provides good team value. The build doesn't generally have stamina problems and Empathic Evasion mitigates a lot of danger from ranged enemies, so I think toughness/health and revive speed are the best stats on curios. You could potentially swap one 17% toughness curio for 21% health on Havoc if you prefer.

Malefic Momentum is a good talent in general, but I don't think it's worth taking here because the build doesn't get enough warp kills to maintain the buff. You lose all stacks if you don't get any warp kills for 8 seconds, and the only warp damage in the build is Kinetic Flayer, greatsword special attack, and Brain Rupture (which will rarely be used). The greatsword special is good, but you need kills to charge it up before it deals significant damage. Overusing the special will also cap out your peril faster and end Scrier's Gaze. Some greatsword builds use Assail for warp kills, but Assail's functionality is mostly redundant with the greatsword's cleaving attacks, and frankly I find Kinetic Flayer too useful to skip in this build due to it's synergy with both the greatsword special and bolt pistol. Greatsword special goes though walls and can be used to proc Kinetic Flayer based on sound cues before you even have line of sight on a specialist enemy.

Warp Ghost gives higher uptime on Warp Splitting, One with the Warp, Warp Rider, and Unstable Power, in addition to improved toughness recovery and extra stamina. This is a lot of value for one point.

Warp Unbound is there to prevent overloading peril when using the greatsword special and force push. Technically you can skip this if you're very mindful about using these actions at high peril, but I don't think it's worth the risk of dying just to save a skill point. Having this node also frees you up to spam these actions when you max peril during Scrier's Gaze, which is valuable in itself.

Warp Speed is a flex node that could optionally be swapped for Anticipation, Just a Dream, Immaterial Focus, or Perilous Combustion. I would only recommend Perilous Combustion if you have another Psyker in the party with soulblaze in their build. I think 20% movement speed for one point is quite valuable in a melee build, so I prefer Warp Speed.