Cut Hordes Like Butter, Hold Giants in Place
 Psyker Build - Warhammer 40k: Darktide 

This build is for high octane gamers who know how to bind their dodge button to their spacebar and jump to left alt. 

The Force Sword MK V is an INSANE melee weapon. Your attack chain vs a horde or small group of enemies should be clicking your charge button, dodging to animation cancel, and then light or heavy attack depending on how much distance or time you have to really pull back and swing. Vs specials, you should atypically go for special charged heavy attacks as those often break the health threshold of human sized specials. Remember to aim for the head when you can. Use lights after charging to stagger and do immense damage, buying you enough time to do it a second time and put them down. Larger enemies should exclusively be attacked with special charged heavy attacks if engaged in melee and you don't need to buy time.

Speaking of buying time, The MK VI Surge Staff lets you throw lightning, and while its damage against anything that isn't Carapace or Flak covered is meager, it can lock down entire waves of enemies. Save for bosses with massive health bars, any enemy struck with this weapons secondary attack will be temporarily stunned. Charging your attack only results in a moderate increase in damage against enemies outside of Carapace and Flak, so I can really only recommend doing this when not under fire, or attacking Carapace and Flak enemies. Spamming your lightning is more important, as it allows your team to strike down defenseless and stunned enemies, or follow up on a dangerous enemy to take on solo like a Trapper. You can either follow up (immediately after casting) your lightning with a special charged melee attack, or dodge back and brain burst them. 

Brain Burst will be your high singular target damage dealer. If you're at max Warp Charge (with this build), you'll be dealing 18% more damage, and with Brain Burst already being an extremely accurate and easy to use long range ability, you can use this to clean up Specials before they get time to approach, or hold right click and gather a charge to instantly gib a Pox Burster as they round a corner. At level 30 upon reaching a boss fight, You should prioritize brain bursting the boss. Kinetic Barrage lets you do an extreme amount of single target damage very quickly. If you want to really kick a bosses ass, take Cerebral Lacerations instead of Psychic Communion at level 15, but I prefer Psychic Communion for passively keeping up warp charges. 4% may seem low, but if you're killing in groups of 20~ then you'll usually at least get one per light engagement, and multiple during holding position stages. It helps to maintain your general damage output because as stated before, your lightning is not very powerful damage wise against many opponents.

A quick overview of the talents selected.

Warp Absorption: Your Force Sword counts as a Warp ability, letting you regenerate massive amounts of toughness by throwing yourself into the heat of things.
Warp Unleashed: Dancing between 80-100% Peril grants you 25% extra damage, and because you have the chance to cool down your Peril just a small amount in between lightning blasts while your targets are still stunned, you can keep yourself in this state for essentially forever. Try to keep your Psykinetic's Wrath handy just in case you fuck up though. You can still cast staff abilities or Brain Burst up to 98% before reaching 100%. One more while at 100% knocks you down in an explosion. 

Psychic Communion: Passive utility to keep your overall damage up through Warp Charges. 
Kinetic Shield: Decent defensive buff if you're playing in high Peril as suggested above. 
Warp Battery: +6% extra damge through Warp Charges. Kinetic Flayer makes your ability to consistantly stun crowds for a period of time less so, and if you don't have the ability to apply Soul Blaze, Wildfire is useless.
Kinetic Barrage: The only feat that doesn't eat your Warp Charges, and lets you kill bosses faster. Quicken might seem good, but now your emergency button removes 18% damage from you, instantly making you weaker.