Chem Dependency Dealer
 Hive Scum Build - Warhammer 40k: Darktide 

After the recent hotfix that gave the Stimm Supply the ability to generate Chemical Dependency stacks, the keystone and ability can now be used together. Something new and unexpected that has happened along with this change (that may or may not be intended) is that 'empty' Stimm Supply bags that are dropped while your Stimm is still on cooldown also provide stacks of Chemical Dependency. As a result of this, Stimm viscosity/cooldown can be maxed without needing to care about being off-cycle on Chemical Dependency stacks since they can always be refreshed with an 'empty' Stimm Supply drop. 

Something interesting about this is how it interacts with other Hive Scum that are running Chemical Dependency as well. Dropping the Stimm Supply provides them with stacks of Chemical Dependency in the exact same way, which means they can also get stacks from an empty bag. This can allow you to completely handle upkeep on your team's Chemical Dependency stacks if there are 1 or more Hive Scum besides yourself on the team (which is going to be extremely common while the class is new). What this allows those teammates to do is to potentially bring stronger Stimms that aren't lined up with the Maxed Out Chems 60s stack timer, since they can rely on you for those stacks instead.

Chainsword? Why? Having an infinite ammo Needle Pistol due to Pickpocket enables you to safely and effectively deal with armor and bosses from a distance without needing to fully engage with them. This gives you some more options in melee if you feel like it. While the Combat Blade and the Dual Shivs still feel very comfortable because of their movement and Uncanny, having a melee weapon that can easily cleave and clear hordes while your Needle Pistol does its job on armor feels a bit more well-rounded. The Chainsword specifically has very high base cleave and an innate attack speed boost that makes the further boost from Swift Endurance feel amazing for horde clear. Combining the Crit Chance you get from Shred, Float Like a Butterfly, and always having 4 stacks of Chemical Dependency together with the extra cleave from Wrath will have you applying Chem Toxin with Coated Weaponry to entire hordes with almost every swing. This contributes to getting your Stimm back even faster thanks to Sample Collector with so many enemies getting hit with Chem Toxin before they die. Also, 60 in Shredder and 80 in Mobility because you will rarely ever be using the special action chain rip to actually kill enemies; its greatest utility is vs human boss/captain void shields since it pops them almost instantly, but 60 vs 80 barely affects its ability to do that.

The Stimm mix can really be anything you want, but I found Fury II (+20% Strength / +15% Rending) + Kalma V (+50% Cooldown Regeneration) to be the most generally impactful to the team. HypeX and Klay can potentially be swapped in depending on the composition of your team. Ability cooldown doesn't matter to you at all, so adjusting around your team is a lot easier.

Giving up the potential +25% Chem Toxin damage while you're in close range from In Your Face is a bit painful, but there is honestly not much leeway for you to give up other nodes unless you want to tank your Havoc survivability or ruin some other major synergies in the build. Since the extra damage boost is only active while you have the Needle Pistol out, it may not factor in as often as you'd like if you're constantly swapping between the melee and the Needle Pistol. If you are dead set on bringing it, you can give up Hive City Brawler or Chem Fortified or even Float Like a Butterfly, but swapping those out definitely comes with consequences.