Extreme melee scum
 Hive Scum Build - Warhammer 40k: Darktide 

[Updated for Depths of the Damned] The Improvised Mk I Shivs are the crux of this build. Being able to be a blender through hordes and elites feels so good. The needle gun is for snipers and for running at gunners. If you enjoy the meditation of horde melee combat, this build is ideal.

The stamina curios are to increase your attack speed with Swift Endurance . With three +3 curios, you are getting +26% attack speed basically always (3 base, +1 from shivs, +9 from curios, times 2%). Additionally, you can block an absurd number of attacks while picking up teammates. You can dodge one regular gunner for like 40% of your stamina with Regained Posture, which is very necessary when you run this much stamina and somehow use it all. You can get the curios by spamming the Mystery Acquisitions at Melk, assuming you've been doing weeklies for a while. Otherwise, check Melk's limited acquisitions daily and Brunt's Armor every hour for suitable curios. 

In play, you are using the shivs nearly 100% of the time. You are dodging around the edges of the horde spamming light attacks at their heads. Or you can just run through the horde faster than they can catch you, dodging as appropriate. When you get surrounded by crushers, just pop a Blackout at your feet and find a better position. Carapace gets heavy attacks to the head instead. Ragers should be going down in one heavy attack or a couple lights while Rampage is up. Hordes of Ragers can be dealt with easily with the increased dodge distance or just using Rampage to hit enough light attacks to kill them before they can do anything to you. Throw a knife when you remember that's a feature of the shivs, then forget about it again for 5 minutes.

The gun comes out when you need to sprint up to the gunners or avoid concentrated fire. If you're out of stamina to proc the ranged immunity, dodge until you have enough, then sprint.  Run 'n' Gun lets you pick off priority targets while closing the gap. Additionally, 5 body shots to a boss will max out your chem toxin, dealing damage over time while you engage it in melee. You'll need to apply additional toxin every 5 seconds to keep it maxed out, and you can use the shiv's special attack to throw a blade to do that. 

Alternative talents: The first thing I usually drop is Pulverising Strikes from the ability. The addition of vanguards to mixed hordes makes cleaving less of a priority to me. Next on the chopping block would be Cheap Shots . You could add Slippery Customer or Street Tough if you need more survivability. 

I also suggest the Skitarius mod to keep your trigger finger healthy. Using the stim and Rampage gets... difficult to keep up with the melee attack speed. My index finger can really feel the burn in an intense mission.