I have a bug in my game (scorpion beta) where one of my vassals' units all turned into Lost Souls. This got me thinking that it would be neat to incorporate a bunch of lost souls around city ruins on the world map that create a "ghost city" vibe, where the previous citizens still remain to haunt the area.
#Ghosts Inhabiting City Ruins
blissful copper
glass oracle
Can infestations inhabit city ruins? I'm pretty sure they can but if not, an undead infestation on some city ruins would fit within this suggestion I reckon