Wasteland raiders coming from the world outside the hive.
Possibly nobility guards and cultists from the upper levels of the hive, with specialists like rebel psykers.
Mutant Beastmen, they have already made Beastmen of Chaos, which prevents them from making them again.
I would like to see the cultists of all the other gods of chaos, united by the dark apostles, with a demonic invasion.
Here is a rough description of the enemies:
The Dark Apostle - specialist who stays out of the fight, loudly reciting hymns to the dark gods, thus summoning squads of cultists while he remains alive. Buffs all cultists, giving them speed.
Possessed cultist - elite, another version of rager. Without armor, half a demon. If it deals damage equal to its health, it falls into a trance, after 1.5 seconds it explodes, causing low damage, summoning a squad of demons.
The traitor psyker - specialist. Casts a mind blast for a long time that deals damage through toughness, pushes it with a psi push when approaching it. After applying 4 Mind Blasts, it will mutate into a Possessed Cultist.
Plaguebearers of Nurgle - Elite, spawns in groups of 2-3.
Slow, no armor, but high health and stun, stagger resistant. Dealing damage adds a curse to health.
Plague Drone of Nurgle - specialist. A huge demonic fly that can fly in to grab you and drag you away from your allies, an analogue of the same fly from Deep Rock Galactic. While grappled adds curse to health over time. It flies not fast, but a lot of health.
Daemonette of Slaanesh - Elite, spawns in groups of 3-4.
They move very quickly, making a dash from melee attacks once every 3 seconds. Dealing heavy damage with a melee attack. If they notice an enemy, they put on a camouflage that blurs their silhouette with purple ripples before dealing or taking damage. Small amount of health. If you look at an uncamouflaged person for a long time, seduction points are imposed over time, slowing down the speed and damage of the character.
Daemon Of Khorne Bloodletter - Elite, spawns in groups of 2-3. Dodges almost all ranged attacks. Skilled in melee combat, blocks and counters with a powerful blow if it blocks a melee attack. Average health, average damage.
Screamers of Tzeentch - Elite, spawns in packs of 1-3.
Levitates in the air, noticing the enemy, swoops down on the victim, causing serious damage in one blow, after which it flies away repeating the approach. Average health.
Pink Horrors of Tzeentch - Elite - spawns in groups of 1-2.
Stays at a distance and fires warp fire. When killed, it has a high chance to split into 2 weaker versions of itself Blue Horrors, each of which can also split into a Brimstone Horror.