Water or Blood
The orphaned aspects of dead gods, mad with time rage and power, twisted to their own dark purposes, considered heretical to deal with in the Empire. A group of them is worshiped in Verona.
They come in many strengths, from the lowest stinking Imps to the greatest of world shattering fiends.
But .. they con only exist in reality when inhabiting a mortal host.
When in such a host it is very hard to detect them, but their are some tell known to those who study such things. when them demon fully manifests it powers it is unmistakable the posses show horns extra limbs, great burning maws, and worse. This inevitably burn up their hosts, forcing them to regularly require new ones.
When exorcised from a host the demon has four breathes to find a new host lest it fall into a vulnerable stupor crystallizing into its essence until the next dusk, dawn, or similar magical event, lest it is warded properly.