The Burning Man - Inferno Guide
 Psyker Build - Warhammer 40k: Darktide 

On Scaling and Difficulty:

This guide is made with Inferno staff and Auric Damnation in mind. I play almost exclusively on that level, and thus my experience and knowledge is entirely relevant to that difficulty. Psyker has a lot of things that scale with enemy density, and nowhere is that more apparent than in this build. Perilous Combustion, Wildfire, Inferno staff itself, Psykinetic's Aura, and Creeping Flames all scale very well with enemy density, meaning you get a lot more value out of this build at higher difficulties.

On Soulblaze:

Soulblaze is a damage-over-time (DoT) debuff the Inferno staff (and Creeping Flames Venting Shriek, and Perilous Combustion) applies to enemies. The Inferno staff applies 2 stacks on a crit, or 1 stack on a normal hit. The important thing to note about Soulblaze is the damage is exponential for the most part, meaning the more stacks you have on a single target, the more damage each stack does. This means you want to increase stacks on an enemy as quickly as possible. Inferno staff can apply a max of 15 stacks, 16 on a crit. Creeping Flames and Perilous Combustion have a max of 31, but it is very hard for anything to survive long enough to get to that max, especially when the application is 6 stacks per cast for Creeping Flames at max and 3 for Perilous Combustion. This debuff can be applied to any enemy, even if the visual is hidden on some bosses.

On the Staff:

The Inferno staff is a powerful tool for the Psyker, able to clear close just about anything in a reasonable amount of time except Bosses and Crushers thanks to the Blaze Away blessing. Optimal configuration is to have the Warp Nexus blessing be the second blessing, but Penetrating Flame is an option if you prefer more boss damage. Penetrating Flame does help with crushers, but it still takes a stupid amount of time to kill them and the real way to kill crushers is to swap to a melee weapon with uncanny, because uncanny stacks will benefit soulblaze (and you'll kill crushers with the dueling sword anyway). If you use Nexus, I recommend swapping the +5% crit chance perk on the staff to either maniac or unyielding. If you use Penetrating Flame, you will want that crit chance perk on the staff. The dump stat (the one you want at 60 while every other stat is 80) is warp resistance for the Inferno staff, as it is one of the only staves that has trouble generating enough peril to constantly use Venting Shriek (which you do want to do, more on that in the ability section). Even without shriek, Inferno has no trouble with peril when compared to other staves (which mostly also want to dump warp resistance, because warp resistance doesn't do a lot). Use the charge/secondary attack on every enemy except ragers and poxbursters. Use the primary attack on ragers to stun them. Don't attack poxbursters, only push them with your melee as Kinetic Flayer may trigger and instantly blow it up otherwise. Use the primary to stun non-ogryn enemies when needed, such as when they are too close to use the secondary.

On the Melee:

I recommend a single target melee weapon with uncanny. You will mostly be using this for dangerous, chonky targets like crushers and mutants. The dueling sword is great at this, and you can also use the Deimos force sword to great effect. Uncanny strike is important because stacks of it boost your soulblaze damage against the most healthy targets, bosses and enemy ogryns. You will generally not need to switch to your melee outside of crushers and bosses. When you do switch for the boss, switch only after applying max soulblaze to the boss (I recommend a mod to show debuffs) as soulblaze damage on bosses is not insignificant for Psyker, who has a hard time doing good boss damage on staff builds. Inferno staff is actually one of the best ways for a staff psyker to apply boss damage when combined with uncanny dueling sword.

For dueling sword, I recommend two of three perks of your preference. Unyielding helps with bosses but you can use Maniac or Carapace. Maniac helps you one-shot ragers (and if you take maniac, I recommend swapping away from Thrust). Uncanny is very much recommended, and Thrust helps one-shot mutants running at you if you hit their weakspot (and one-shot maniac ragers with full stacks of both Thrust and Uncanny). Other good secondary blessings are Agile (defensive), Riposte (offensive), and Relentless Strikes (bosses). Rampage is a bad pick since you don't want to horde clear with dueling sword, you have a horde clear staff anyway, and Precognition has the issue of a very short duration with a finicky activation.

On Blitzes:

Brain Burst (BB) is a tool you never want to take out. It is your last resort, used only because nobody else is around to take out the sniper 90 meters away. In any other case, you would be better served by slide-spamming up to an enemy and lighting them on fire. This build is an Inferno build, and focuses on Inferno damage. Use the Inferno staff. BB is always a damage loss, and the amount of investment required to make it more worthwhile simply isn't useful. BB is by far the worst blitz on the Psyker, and I don't recommend ever trying to rely on it if you can help it.

That said, you can easily make a more BB-focused build work. You could swap Kinetic Flayer for Kinetic Resonance to speed up BB after ability use, or go Empowered Psionics over Warp Siphon for more consistent BB use. If you do go EP, don't take Bio-Lodestone or Psychic Leeching, as there are better nodes elsewhere to take. Crystalline Will on the way is obviously a crutch I wouldn't recommend if you're pushing into Aurics.

For alternatives, Assail is a choice. It doesn't have the range that BB has but it's a lot more useful, the only problem being much of that use is covered by Inferno anyway. You also lose out on Wildfire and Psykinetic's, which is quite devastating. The Inferno staff will still largely work, though, so you can take Assail if you strongly prefer it, it just isn't optimal.

Smite is not a good choice. Empowered Psionics Smite has largely the same effect and role as Inferno when combined with Creeping Flames (albeit at a slower but safer pace) while Smite without EP is just a stun, and most things in stun range will die to Inferno. As with anything, you can run whatever you like with enough skill but I do not recommend Smite at all for Inferno.

On Abilities:

Inferno staff makes good use of two abilities, Creeping Flames Venting Shriek (henceforth referred to simply as Shriek since Warp Rupture is so awful I never recommend it) and Bubble (Telekine Dome). Shriek should be used when your peril is above 85%, allowing you to apply 6 stacks of soulblaze to basically everything in front of you for 30 meters. It stuns ranged enemies, which is quite helpful, and amps your soulblaze damage. Shriek is one of the most damaging and helpful abilities, and if you are looking to carry a group I highly recommend spamming it. Bubble is useful if you want to play defensively and help your team stay alive. It can keep your team alive in a pinch and invalidate a lot of specials from taking your team out of the action, including bombers (fire bombers can't cover the bubble's insides in fire unless they threw a bomb before you used bubble, you can sit inside the bubble with pox gas and not take damage anyway due to bubble's toughness regen though I don't recommend this). Telekine Walls are less useful because they only help in corridors where you can burn everything in one direction anyway, and Scrier's Gaze boosts your damage but not nearly as much as Shriek (you already burn everything to death in Inferno distance anyway, Shriek goes beyond that).

About Wildfire:

Some people dislike Wildfire, but it is good and is a damage increase. Wildfire works by spreading up to 4 stacks of soulblaze on a target that dies, with each stack being distributed evenly (so a dying target with 3 stacks spreads 3 stacks, 1 stack to each nearby enemy if there are 3 of them with 0 stacks, but will spread 4 stacks if the dying target has 4 stacks, 2 to one of the 3 nearby enemies). Wildfire is incredibly useful because it can spread beyond your Inferno staff's range, meaning when an enemy enters Inferno's range you already have 4 stacks applied to them when in tense, Auric Damnation-level situations due to enemy density being stupidly high. That is 1/4th of Inferno's max stacks, which is significant and really helps Inferno stack all that quicker and kill quicker, helping Wildfire spread more. On top of that, Wildfire helps eliminate chaff (4 stacks doesn't kill alone but can kill with Blaze Away and other buffs) and manage your sides/back without you doing anything. You won't be killing hordes with Wildfire, but when you turn around to face a threat you'll find enemies nice and pre-toasted. It also helps you gain more Warp Siphon stacks through In Fire Reborn. I wholeheartedly support Wildfire on an Inferno build in the game's current state on Auric Damnation (and it's still very good on a lot of other staff builds with Creeping Flames too).

About Soulstealer, Mettle, and Empathic Evasion:

Generally, the node I'm 'swapping' for Empathic Evasion is Soulstealer. Mettle and Quietude provide enough toughness in most situations with the Inferno when combined with Empathic Evasion that you don't really need Soulstealer, specifically because Mettle still goes crazy with Inferno due to how Inferno is lots of little hits. You can easily drop Empathic Evasion for Soulstealer if you prefer.

About Empyric Resolve and Penetration of the Soul:

Empyric Resolve (ER) is a great node for every other staff. It helps a lot with peril generation, which enables you to spend a lot more time dealing damage rather than quelling. Its malus is significant, but on Auric difficulties Psyker tends to die if they get hit in rapid succession, which is the only scenario in which the toughness replenishment would matter (because at other times you would have the time to regenerate to full anyway). Basically, if you have trouble with ER's malus I recommend working on your dodging/sliding until you don't. You can definitely feel ER's malus, but if you're good enough then it's practically not a malus at all. The issue is Empyric Resolve is too good for Inferno, which will have trouble generating enough peril to constantly shriek with ER involved, and shrieking constantly is far more important than an extra charge or two of Inferno before quelling (especially when Inferno spends less time quelling than other staves). At the high end of skill. ER is still a net positive, it's just a big hassle on Inferno.

Penetration of the Soul (PoTs) is a bad node if it even worked. Veteran gets 10% rending at a similar point in their tree with no conditions whatsoever. 10% rending at 75% peril is mediocre even if you are a great Psyker that constantly stays above 75% peril. Oh, and the node is currently bugged so it doesn't even work. The only reason to take PoTs is because it's not ER. 

About Curios:

Curios and their subperks are a hot topic. I have simply provided my preference and recommendation. Use what you find works best for you and your playstyle/purposes, as curios should be shoring up your biggest weaknesses. Toughness Regen Speed is good for newer players and is something to get rid of once you are good enough to start clutching. You generally want to get 201+ HP so you can take enough poxbursters to the face without dying.

About Edging and Quell Cancelling:

'Edging' is when a Psyker tries to stay at high peril constantly for talents like Warp Rider and One with the Warp. It's useful, but unnecessary. You can play on Auric Maelstrom without edging at all, but it will be more difficult.

Quell Cancelling is when you quell for a small moment in between primary attacks, speeding up your attacks through animation cancelling. It is completely unneeded, and I never use it, but you can and it will help, though not that much on the Inferno.

Nodes to Drop:

Not every node is important in this build, and if you feel like something isn't working for you, change it. The least useful nodes are Kinetic Deflection, Empathic Evasion, and Kinetic Flayer. Empathic Evasion is very useful, but can be substituted with slide-spam and positioning. Kinetic Flayer is a very minor damage bump over Warp Battery and not super useful. Kinetic Deflection is mainly for use in really bad moments when you don't even have time to use your staff such as when a boss is aggroed on you.

Nodes to Pickup:

Some nodes that would be pretty nice to have are: Soulstealer (defensive, more toughness), Warp Battery (offensive, more shriek and more damage but inconsistently helpful), and Kinetic Resonance (helps make BB feel better, still a highly preferential pick and not my recommendation).

Maintaining Blaze Away:

Blaze Away is a powerful and important part of Inferno damage. Some like to spam primary attacks or minimum-charged secondary attacks, which manages to maintain Blaze Away stacks. However, Blaze Away stacks incredibly quickly, to the point where you only lose about 200 damage per fully-charged secondary (comparing between maintaining Blaze Away and not maintaining Blaze Away at full Soulblaze stacks). This is quite insignificant, and thus it is not necessary (and even suboptimal) because the upside of fully-charged secondaries is much faster application of soulblaze stacks which is more important for overall damage.