Warp Wraith
 Psyker Build - Warhammer 40k: Darktide 

The Warp pulses through your veins, boundless ethereal energy strengthens every muscle, quickens every reaction. Your mind is master of the materium, you sense every molecule around you, the very heartbeats of your prey beating in the distance. You are a Wraith of the Ordo Nephilim. 

Summary - A relatively high mobility build focused around melee combat with Talents like Warp Expenditure , Mettle , Empathic Evasion , Just a Dream , Warp Ghost , Kinetic Deflection providing reliable passive defensive buffs and solid Toughness regen. 

Strategy

Focus on being aggressive in melee against human sized enemies with Atrox Mk VII Tactical Axe, use push attacks to create space when needed, otherwise spam dodges and light attacks for best use of Brutal Momentum as Mk 7 light attack pattern has good horizontal attacks mixed in for easy head chopping. 

If there's a Bullcharge Ogryn, Martyrdom Zealot, Rampage Scum or Break the Line Arbites, let them lead the way instead unless they repeatedly die. Focus on being anti Specialist, anti Gunner, and Ogryn control with Electrokinetic staff. You can frontline with this build up to Auric/Maelstrom but being in the thick of melee combat often may increase the chance you miss high priority threats like Bombers or other Specialists. 

Dreg Rager Scab Rager - Special attack to the head with Tac Axe (Taxe) stuns one, against multiple use a corner or doorway to reduce the amount of Ragers attacking at once. Use Push attacks frequently against them, also mix in dodges if they begin their chain attack animations. If you're not confident fighting multiple at once in melee use Electrokinetic secondary to control them for teammates. 

Scab Mauler - Special attack to the head, spam special attack to chest Flak weakspot, alternatively Electrokinetic Primary to chest weakspot melts them. Let teammates deal with groups, spam half charged Electrokinetic attacks to control the Mauler groups for teammates. 

Bulwark Almost always ping for team, use Electrokinetic secondary to stun lock them. Prioritize them over other melee Elites after dealing with any ranged Elite/Spec threats as they interfere with your teammates' cleave and are an absolute nuisance to melee focused players.

Also can use primary Brain Burst on them if Flayer is available for an easy OHKO.

Crusher - Always ping for team and stunlock with Electrokinetic until you're very confident with Taxe. If one Crusher manages to sneak up on you, get real close to him so he can't use overhead and use dodges while attacking his head with Taxe. 

Never engage multiple Crushers at once in melee in an open space. If clutching, kite Crushers with slide spam Taxe heavies to create distance, ignite barrels around them and Electrokinetic secondary to lock them down but always keep distance.

Scab Gunner , Dreg Gunner, Reaper - Spam primary Electrokinetic to suppress them down, or if possible spam Taxe slide plus heavies to close gap and wreck them. If you're pressed in melee by a horde while they're in Volley mode, Empathic Evasion can keep you safe for a bit while you reposition out of their sight. 

Scab Plasma Gunner - Secondary Electrokinetic to stun them, then primary to their Flak chest weakspot. Melee will work well against them too and forces them to put away their Plasma gun. 

Scab Trapper - Electrokinetic Primary spam to head or one full Secondary Charge if they're in the open. Aim a little above their head when using Electrokinetic Secondary to zap them behind a horde. 

Pox Hound - Full charge Electrokinetic Secondary or bait the pounce and dodge with Taxe. Taxe push attack timed right also stuns them if they pounce.

Scab Flamer Dreg Tox Flamer ,Dreg Tox Bomber Scab Bomber Scab Sniper - Full charge Electrokinetic Secondary, or primary to the head if out of range. Bombers are the highest priority enemies, they need to be gone yesterday as their flames/smoke obscure dangerous Elites/Specs, encourages teammates to break Coherency and reduces the area you're able to fight in. 

Chaos Spawn Plague Ogryn Scab Captain - use Taxe and dodges, learn their attack patterns. If with teammates, focus on Specialists/Elites while they fight boss as they'll probably deal more damage than you and Specialists are way more dangerous than a boss. 

Scrier's Gaze - use when fighting hordes for excellent damage, max out Precognition with Taxe then spam Electrokinetic primary/secondary during Warp Unbound depending on if there's Crushers that need controlling or Gunners that need to die.

Disrupt Destiny Your feet have wings everytime you kill a marked target, use that to your advantage as you zoom around between events from target to target with Taxe. During events, use your Electrokinetic primary/secondary to keep stacks maxed when possible, but resist the urge to break Coherency - fight more defensively.

Curios: For Psyker Combat Abilities are extremely powerful so you'll want to max out CD by running triple CA Regen perks. 

Triple Revive Speed is also highly recommended as your game becomes eexponentially more difficult with every player down. You're most vulnerable while reviving/rescuing players, so shortening the time it takes to do that is a no brainer.   

The last Perk is up to you, though I highly recommend double Stamina regen because Stamina is aabsolutely critical to Darktide melee combat and melee combat is easily 80% of Darktide's combat. Block Efficiency is great for rescuing players, extends the time you can withstand attacks while reviving. 

Other Survival Tips: 

Besides staying in Coherency, prioritize chokepoints like rooms, narrow hallways and doorways during ambush events to stay alive rather than fighting in the open where Snipers, Bombers, Gunners will cause headaches for you. 

Have fun, reject!