The Tertium Lawnmower
 Hive Scum Build - Warhammer 40k: Darktide 

Heretics get the hell off tertium now

This is a pretty straight forward build: Rampage! , Stim if you can, and swing wildly into crowds of enemies and watch heads fly. The Shivs can pretty reliably take down just about anything but does struggle a little with carapace. However with Coated Weaponry and some good dodging its fairly easy to chip even crushers away without taking a hit. You are still a glass cannon and very squishy, so dodge often..

Improvised Mk III Shivs 
Even before the nerf to the MK 1's cleave these are good, just require a little more effort for those single targets. Even without popping your stim using Rampage! and using pretty much exclusively light attacks will carve through pretty much any horde.

Attack Combos:

Hordes: light attack, shove occasionally

Single Target: Push-Counter Attack-Heavy Attack. Use mostly on Ogryn enemies and anything with armor. Each hit after the push is a jab that is good to shove directly into any special enemies face.

Bosses: Do whatever, dodge often, only directly engage if you have Rampage! active. Your single target combo will be good damage however using your light string to proc Boiling Blood occasionally will basically make it so then entire boss fight is done while Rampage is active

Ranged Weapons: 

Branx MkVI Needle Pistol is always a good option for dealing with elites and especially crushers. Running Stripped Down allows you to disengage pretty easy and Run 'n' Gun allows you to tag targets without being lit up yourself. 

Godwyn-Branx Mk VI Bolt Pistol Is a slightly less effective but much more fun option. Using Leathal Proximity and Puncture makes it good at range and up close. Most fun when shoved into a random horde poxwalker and fired point blank to stager the entire front line.

Curios:

These are just what I personally run. Change according to your play style but keep the one Stamina Curio with stamina regen buffed. You will need to shove-counter attack a lot.