Batty's Gingerbread Man
 Hive Scum Build - Warhammer 40k: Darktide 

Main interaction is relying on Catachan Mk VI Combat Blade extremely high Finesse damage and Hyper-Critical to maintain high crit chance to oneshot as many enemies as possible, and Splash Damage with Virulent Strain to keep toxin stacks on as many enemies as possible to substantially buff you and your teams damage. Bleed/Toxin DoT does NOT activate Splash Damage, so make sure to try to kill elites outright with melee attacks, Hyper-Critical makes this much easier. You also don't want to grab both Hyper-Critical and Hyper-Violence as they counter each other, with Catachan Mk VI Combat Blade having such high Finesse and how easy it is to maintain high crit chance, Hyper-Critical is the better option for what I want, but Hyper-Violence can work as well if you like ramping damage. 

Catachan Mk VI Combat Blade push attack is extremely fast with extremely high Finesse damage and has a stronger version of Uncanny Strike than the Shivs, offering 120% Rending compared to Improvised Mk I Shivs 40% Rending at max stacks. Rending and Brittle gives bonus damage past 100% penetration, so for singletarget, spam push attacks and aim for weakspots. When Uncanny Strike is fully stacked, this allows you to solo a Daemonhost easily. DoT also retroactively inherits Rending from Uncanny Strike, meaning you can shoot your Branx MKII Needle Pistol to apply many Toxin stacks, switch to Catachan Mk VI Combat Blade, and stack Uncanny Strike quickly to drastically improve the Toxin DoT while applying Bleed from Flesh Tearer and doing massive Finesse damage from the hits themselves. 

Float Like a Butterfly activates on dodging shooter gunfire (not Gunners) as well as melee attacks, so has high uptime of crit chance. You can take Finesse damage buffs in Stimm Lab for much more damage instead of crit chance but I like the constant proccs of Hyper-Critical. 

Change perks of weapons to your liking, if you want more Monstrosity damage, use Unyielding. You can kill a Daemonhost without getting hit without Unyielding though, so I prefer the reliability of Flak for oneshots and Carapace to deal with groups of Crusher which you can wreck thanks to 120% Uncanny Strike Rending push attacks and Scums' many substantial damage buffs, such as Virulent Strain frequently active from Coated Weaponry and very high crit chance uptime.

For Monstrosity DPS, activate Stimm if available, shoot 6 shots of Branx MKII Needle Pistol in yellow mode aiming for weakspot (crits + weakspots give more toxin stacks), activate Rampage! for Forge's Bellow stagger and spam push attacks at weakspot. 

For Daemonhost, do same process above except wait for it to start first attack animation to activate Rampage! for Forge's Bellow stagger. 

I keep Branx MKII Needle Pistol in blue mode unless there's a Monstrosity; enemies spread toxin when killed but the darts do not stack how much spreads from a single enemy, meaning 6 darts into a single enemy wont spread 6 darts worth around them when killed, so try to aim for easy to kill enemies and hit as many different enemies as possible to shotgun hordes. This can give you your Stimm back extremely fast from Sample Collector, be aware your Stimm needs to be on cooldown to reduce the cooldown, kills when your Stimm is active do not count towards reducing the cooldown of the next. You can dump Damage stat on Branx MKII Needle Pistol since that only affects the dart damage, not the Toxin stack damage.

You can drop Jittery for whatever you'd like, I consider it mandatory from how strong it is but your playstyle may not utilize it as much and the point can be spent better elsewhere. Good options are Channelled Devastation which will always be fully stacked thanks our high crit chance, and Toxic Renewal for extremely good toughness recovery thanks to our existing focus on spreading Toxin, but there's a bunch of options. 

Curio perks can be whatever you want, though stacking any % gives diminishing returns as it's multiplicative not additive, so 20% Gunner Resist 3x does not = 60% Gunner Resist, instead it gives around 50% Gunner Resist total.