The Poltergeist (Auric Maelstrom Stealth Hammer Build)
 Zealot Build - Warhammer 40k: Darktide 

TL;DR:

If you want high single-target damage and CC, with great survivability and clutch potential to go along with some group crowd control and horde-clear capabilities, The Poltergeist has you covered all the way up to Auric Maelstroms.

Gameplay loops and tips:

- Thunder Hammer big bonk out of Shroudfield on monstrosities, Skullcrushers, Bulwarks and Maniacs. Maniacs in particular should be a sidestep and one-tap situation. For the inexperienced: try to get stacks of momentum from Inexorable Judgement before stealthing and hitting weak spots with the charged heavy attack. It's not quite the one-taps of the 1HP Martyrdom champs or most pre-patch 14 Thunder Hammer builds, but if done right Monstrosities should go down within 3-4 hits max (and often 1 or 2-taps) without having to sacrifice your HP bar. Thrust is of course a must-have blessing on the Thunder Hammer, but Momentum can be swapped out for Headtaker if you wish to trade some frontline sustain for more firepower.

- Agripinaa shotgun slugshots (preferably headshots) on Maulers, Ragers and even Skullcrushers, both for outright killing them or just knocking them down/staggering them to create space and breathing room for yourself and team mates when a group of them are approaching fast. Same of course works for Bulwarks - slugshot stun on their shield to create an opening for the team, or for yourself to finish off with either a follow-up slugshot to the head or a thunder hammer bonk before they put their guard up again. For my fellow Zealots out there that run Blades of Faith, the Grippy slugshot is effectively the equivalent on this build to take out priority targets from a safe distance.

- Big clutch potential from Shroudfield's stealth and Until Death. Stealth and non-stealth backstab kills with the TH to quickly gain the cooldown reduction from Pious Cut-Throat, and use Shroudfield proactively to reposition or pick up downed allies. For the newer players: it doesn't always have to be a backstab out of stealth, sometimes it's more important to just bail out of a bad spot, particularly on Auric Maelstroms. Until Death is there as a secondary get-out-of-jail card either for when you do get caught in a bad position and Shroudfield isn't available, or if you're trying to rescue allies in a do-or-die situation and likewise, stealth isn't an option and you're already low on health.

- Immolation Grenades to help set up kill zones in choke points for horde/add clear, to take out gunners grouped up in the distance, and to clear space when clutching a rescue on allies (throw grenade at or near captive allies, then stealth for the revive/rescue.) Fairly straightforward stuff.

- In a nutshell, you'll be spending time more or less 50/50 between the Thunder Hammer and Shotgun. Get into a good rhythm with Slugshot and Slugshot as much as you can on priority targets before going in and finishing off everything with the TH. Spam regular shotgun rounds only as a last resort to stagger something immediately away from you or to briefly interrupt gunners lighting up your team. Use Shroudfield either when absolutely necessary to clutch up and/or to avoid going down, or when you know you'll have an opportunity to recover it fast before the next wave of enemies shows up (e.g. before jumping into an elevator or moving between areas, when you see an opportunity to dodge around the back of elites and poxwalkers with the Thunder Hammer for the backstab kill CDR, and so on). Naturally, the higher the difficulty/modifier the less carefree you can be with Shroudfield. Use it wisely.

Build Variants:

There are of course some possible variants for this build, there's definitely at least 1 or 2 talent points that can be moved around according to tastes. Fortitude in Fellowship can be replaced with Disdain for extra damage output, or Good Balance for the 25% damage reduction on dodge if you feel like you need it, or even just the 10% extra health below Faithful Frenzy if you want more HP. Out of the two keystone modifiers, this build does enough damage as it is and so I personally favour Retributor's Stance over Inebriate's Poise overall just for the very accessible (can even be proc'd at range with the shotgun) toughness regen boost every 8 seconds. Essentially the core aspects of the build are a good Thunder Hammer, a complimentary ranged weapon, Purge the Unclean, Shroudfield, the Pious Cut-Throat cooldown modifier, Inexorable Judgement and Until Death. Everything else can be changed or moved around to some extent. The must-have perks on the Curios are two Sniper damage reductions, one Gunner damage reduction, at least one 10% revive speed and at least two 5% toughness and one 5% health. Same situation with the traits: there's at least 1-2 perks that are more of a choice than anything else. Swapping the +1 wound for a health % Curio is also a viable alternative.

Secondary Weapon Alternatives:

Other possibilities for secondary weapons: there is a variant with the Kantrael shotgun for less ranged, single target CC and DPS but with the extra horde-clear, soft group CC and Bulwark-killing potential that the Kant brings to the table. There's also the post-patch 14 Columnus Infantry Autogun for the high RoF, DPS on specialists and great ammo reserves but more importantly, as a useful alternative for Lights Out missions with its flash light.

Summary:

All in all, this build should serve you well both in close combat and from a distance. Always try to have a slugshot loaded into the Agripinaa shotgun if possible and at the very least 3 or 4 regular rounds too. Pick off and/or knock down as many elites and specialists from a distance with the slugshots, whether it be gunners at the back of the room or maulers/crushers tucked away in a mixed horde and then move in with the Thunder Hammer to clean up or pick off any remaining elites if necessary. For Poxhounds - if it's a lonely stray then it's one slugshot and job done, but if it's a pack of them, you're better off unloading the regular rounds into them and ideally, from a far enough distance into a chokepoint (in other words, not when they're around you and right on top of you, otherwise you're better off switching to the TH and keeping your guard up ready to block them away). An alternative name for this build could honestly be 'the insurance policy' as typically, if your team can't deal with multiple elites and specialists and/or monstrosities from a distance and at a fast pace, you either CC or put those enemies down yourself. Add in the Shroudfield clutch and indeed, you will at times be your team's backup plan and last chance. If you apply good situational awareness, the ability to effectively prioritize and acquire targets fast, and know how to move, where to stand, when to dodge, reposition and block or push foes back then you'll be neutralising everything from both near and afar, ghosting to your allies' rescue and showing monstrosities the afterlife.

Have some karkin' fun with this one, Varlets.