Greatsword Psyker (Bound by Duty Update)
 Psyker Build - Warhammer 40k: Darktide 

TLDR: spam the greatsword special attack + hit things with the blade part not the warp slice part

Bound by Duty Rework: melee pysker is goated

Malefic Momentum + Unstable Power + Warp Rider + Disrupt Destiny combine to give you massive damage, keep your peril as high as possible at all times. Charged Strike damage and Covenant Mk VIII Blaze Force Greatsword special attacks (both the sword slash and the warp slice) count as warp attacks for Malefic Momentum. And the sword has a moveset perfect for getting weakspot kills on the blue glowing enemies for Cruel Fortune 

Your general play pattern should be use the Covenant Mk VIII Blaze Force Greatsword special attacks to generate all your peril. The warp slice part of the attack deals barely any damage, but the slash with the sword itself is incredibly powerful. It does more damage than its heavy 2 and 3 strikedown attacks, with massive cleave, generating massive peril. On its own the special attack doesnt need the cleave from Warp Splitting but thats basically your only horde clear, which is just more incentive to keep using the special attack. Aim for heads, you get tons of weakspot damage from Disrupt Destiny and get weakspot kills to quell. DO NOT waist time trying to charge it up, the charged version is not worth giving up the peril you gain from just using it. High peril is how you stay alive and how you deal damage. If you feel like you arent doing enough damage, make sure you're staying above 80% peril. However, the energy slash, even uncharged, deals decent stagger, so use it to interrupt gunners and specialists, giving you time to reach them and kill them. It goes thru walls, so use it to stagger enemies behind cover, trigger Kinetic Flayer and to get a Pox Hound off of your teammates. The push attack is a very nice stab, great for targeting heads and it knocks back Bulwark shields really easily, but its slow to come out so dont use it unless you need to.

SLIDE like crazy. Sliding is your best way of moving around, since most of your speed comes in short bursts from Mettle and Disrupt Destiny sliding helps you maintain that speed to go from enemy to enemy. Definsively speaking, dodge until you cant anymore (about 9 times) then block long enough to recover your dodges. 

Against bosses, focus on heavy strikedown and special attacks, using the special pretty much as soon as you dip below 100% because it does better damage, but against warp shield bosses save it for a bit longer to have it ready when their shield goes down, then slide in and slash. ForChaos Spawnand Rinda Karnak (the sword lieutenant) if they're targeting you just play defensively, block, dodge, and kite them as best you can. Solo-ing them is somewhat difficult, but you can whittle them down if you have enough room to kite. If you have any other enemies to deal with and you can kill them easily, use that to keep your toughness up. Once they go for your allies start going single target damage. For Beast of Nurgle Rodin Karnak (the gun lieutenant) and Scab Captain keep them in your shield to block ranged attacks. For Plague Ogryn just block and dodge its swipes and put the poor thing out of its misery, but dont let it push you into a bottomless pit.

The ranged weapon can basically be whatever you want Zarona Mk IIa Quickdraw Stub Revolver Godwyn-Branx Mk IV Bolt Pistol (either mark) Agripinaa Mk VII Combat Shotgun Accatran MG Mk II Heavy Laspistol are all good options, if you prefer the staff basic attack any except the inferno staff are good too

Try to use Telekine Dome more offensively, take space and block off gunners and more importantly Scab Flamer Dreg Tox Flamer Scab Sniper and Scab Trapper from harassing you while you fight in melee. Also use it to let you push gunners to actually kill them.

Note the sword's warp resistance stat should be underleveled. The weapon I use has 45 in the stat, even less than that would be preferable, but I would be cautious about going too low, I like being able to swing it 3 times to reach max peril, as you do need to get weakspot kills to quell. You can replace the staff with whatever your favorite ranged weapon is.