Greatsword Show ( Havoc 40 )
 Psyker Build - Warhammer 40k: Darktide 

Build Alternatives :

1. The Covenant Mk VI Blaze Force Greatsword have multiple great variation of blessings to go for depending of your desire use. Considering you are using Scrier's Gaze making your Peril high almost all the time, Unstable Power gets a lot of value, and crit being so strong nowadays makes Riposte an exellent choice. But ! Deflector ( paired with Kinetic Deflection ) will allow you a more versatile approach to gun fights or heavy fire towards you; Precognition works wonderfully with Scrier's Gaze + Precognition + Disrupt Destiny, Shred bringing you higher crit chance in fight but less consistency than Riposte; Blazing Spirit allow you to stack soulblaze easily. I wouldn't advise to go for Wrath nor Warp Sliceas they make no significant difference in an actual fight, opposed to all other Blessing listed above.
2. You can swap around Unyielding and flak damage at will on the Covenant Mk VI Blaze Force Greatsword depending of your need and desires.
3. If you feel the need for more anti range options outside of talents, you can swap Infernus for Ghost on your Accatran MG Mk II Heavy Laspistol. Your damage will be reduced and you won't stack burn on targets anymore ( reducing your Monstrosity damage ), but you will be able to run trough waves of gunners without any issues.
4. Just a Dream and Warp Speed are two nods that can be changed for something else depending of your desire. Keep in mind before changing that they give you both survivability and insane mouvement speed ( with the Accatran MG Mk II Heavy Laspistol equiped ). Here are your options : Empathic Evasion to allow less gunner pressure ( won't be active all the time but will still make you avoid a non negligeable ammount of damage from range. ); Immaterial Focus giving you better survivability at high peril ( which you basically always are with the constent Scrier's Gaze activation. ); Vulnerable Minds for stronger damage output against priority targets. ; Warp Ghost to keep your peril high all the time which will also keep your buff high; Perilous Combustion to add to your damage range DoT damage on large radius and finally Kinetic Resonance ( POP, POP, POP... need i say more ? )
5. You can swap on two curios Revive speed for damage reduction against gunners if you ever feel to weak against range situations.
6. You can swap one Toughness Curio for one Stamina curio depending of how much you use Kinetic Deflection and pushs.
7. Lingering Influence and Perfectionism are interchangable, one giving you better more consistent stacks while the other one giving you higher damage on large horde spawn ( Allowing you to reach the 25 stacks ). Keep in mind that Perfectionism is more suited for Gun psyker, which you aren't.

Strength :

• You apply strong melee elite damage which evolve into large horde clear once the special ability of the Covenant Mk VI Blaze Force Greatsword is fully charged, killing up to 100 enemies in one slash.
• Armor Targets outside or Rotten Armour die easily to your heavy attacks making you a great priority target clearer.
• You possess strong and extremely consistent boss damage on your own
• You are quick on your feet. The combination between Warp Speed and 80% mouvement speed on a vanguard weapon ( Accatran MG Mk II Heavy Laspistol being one ) make you run around the map at very high speed. Changing positions, pressuring away targets and helping teamates becoming much easier.
• Both the Accatran MG Mk II Heavy Laspistol and Brain Rupture will give your team a low cost high damage range option when needed.
• Kinetic Deflection Allow you to hold a long longer against relentless onslaught like Chaos Spawn or Dreg Rager.

Weakness :

• You keep the squishiness of a psyker while leaving the safety of it's usual range options or toughness regenerating options, making you extremely vulnerable. Perfect positioning will help you to a point, but  you will often end up in situation that you simply cannot fight against alone.
• Even so your mouvement speed can play a large part in saving games, if you ever end up alone, your clucting potential is extremely limited. Between your lacking survivability, your slow building horde clear and your slower more methodical approach to boss encounter, you lack significant options to save a game.
• You might be perfectly able to deal with armored enemies but as soon as a Rotten Armour mission hits you, you simply cannot deal with a Scab Mauler in less than 7 Heavy weakspot hits, not even speaking of Crusher.
• You occupy a melee spot without possessing large stagger abilities or strong survivability. You also occupy a Psyker spot without giving the usual insane and easy to access horde clear making team building much more precise and complicated. Basically you will need a golden toughness giver and a horde clearer outside of you, which would be your usual role as a psyker.
• The usual ammo economy of a team take into account a Staff psyker. Staff psyker that you aren't. Every ammo you use is precious, even more so if your team doesn't possess a Veteran.

Conclusion :

Even so Melee psyker used to be quite strong, we actually never see it nowadays. Definitly a weaker version of the otherwise completely broken Psyker that we all know about. 
Yet, So refreshing to play, so refreshing to see, so interisting to build around and play around. Is it gonna win you every game ? no. 
will you be able to save games easily ? absolutly not. If you are the type of person that is generally the last one alive, picking this build up will actively make it harder to win. But so what !

It will simply give you a different type of fun, outside of any meta idea and that is more than always welcome !

Might not be as original as other of my builds might be, but still a pleasure to create and actively try out. 

N.B.

This build is still very strong, and even so it'll require some team adaptability, you won't have issues even in the highest havoc level. Havoc 40 can become rough, but this build can and will carry trough havoc 30-35 without issues !

I encourage you to try it out and tell me what you think ! ;) ( Giselle5957 on discord ;) )