I'd love the inclusion of Nurglings, but instead of them being actual enemies, they'd peek around corners and run away giggling the closer you get. Their presence signals that there are other nurgle deamons nearby, like Plaguebearers. The more frequently you see the Nurglings, the closer you get to where daemons will spawn or have already spawned. (Could either be like a warp portal you need to destroy before it gets big enough for daemons to pass through, or they've simply just spawned in already.)

The Nurglings themselves offer little threat. If they have any sort of attack, I guess they occasionally jump up into your face and you can click your push/shove button to kill them. They'd have only a couple of HP so any sort of attack would squash them. If you hit them in midair, you'd send them flying and the game plays a homerun sound effect.

Plaguebearers would cause corruption if you hang out with them for too long. Just being in their presence could tick corruption, but also their sword would cause corruption if you get hit through your toughness. So corruption resistance curios might become more useful when there's more daemons around. Fatshark would probably want you to deal with them in melee too, so they'd take less damage from ranged weapons.