Stimm Maniac
 Hive Scum Build - Warhammer 40k: Darktide 

Using both of the Crowbar's modes for either horde control or Elite+Special+Boss damage allows you to be a decent all-rounder and adjust yourself to deal with almost any situation. The MkII Needler Gun offers a spreading on-death alt-mode toxin, letting you spike a few headshots around in a horde to take advantage of Toxin Mania and Sample Collector to make good use of the blunt-mode crowbar's wide sweeping heavies to very quickly get your stimm off cooldown.

Honestly, you can use whatever blitz you want. I prefer the chem bomb for the outright broken area denial it has despite the anti-synergies with Pocket Toxin . Blackout and Boom Bringer both provide good clearing through Pocket Toxin , with the first being geared toward a quick stun which is very nice utility against Gunner/Reaper/Rager groups and the second being pure damage against bosses and monstrosities.

Sample Collector paired with Chemical Dependency, even if you opt into a short duration for +1 stack max using Maxed Out Chems, can reliably keep you at full stacks for an entire mission as long as you keep killing and spreading toxins. On top of the basic keystone, grabbing Chem Fortified  gives you easy access to a nice +15%(+20% with Maxed Out Chems) Toughness Damage Reduction, which is useful for packs of gunners and reapers; Alternatvely you can grab Chem Enhanced for a whopping +15%(+20% with Maxed Out Chems) Crit chance, netting you an easy 45%(50% with Maxed Out Chems) crit chance as a baseline not even factoring in any blessings or stimm choices, giving you a steady source of tox applications through Coated Weaponry.

Spur(up to 2) gives a great selection of utility effects for a very low cost in added cooldown, but 3 and 4 are useful only in stepping stones to the capstone choice. Wildfire is a good general choice for damage and since we sit at ~50% crit as a baseline as long as we're stimm'd up and perfect block or dodge(as you should be doing, honestly), the extra Finesse from Wildfire 4+5 get a lot of mileage, but the fury capstone line giving Rending is also a fine choice. The only reason I take the toughness line in the Cartel Stimm Lab is for a 16% Damage reduction across the board, the toughness regeneration is fine, not great but not terrible. You can opt to drop the entire line to lower your cooldown, if you want. Kalma with the cooldown reduction isn't really worth taking, you can keep Rampage! up basically indefinitely for hordes and bosses, and a lot of the time the span of time between when you really need to bust out your ability is long enough for them to come off of cooldown anyway.