A demon that has escaped from the Abyss of the Bastard into the world of matter cannot exist without a being of matter to lend its intelligence and strength. It cannot, by its nature, create such order for itself – only steal it.
Corners seem to be one of the most vulnerable places for demon intrusion, and as such many holy sites are formed of perfectly round structures. Eggs, also, are a powerful and precious symbol that can also become a gateway for the birth of a Demon into the world of matter, with the proper spells and sacrifices. A demon newly brought into the world has no intelligence, no language, and no subtlety to speak of – it can only leap into the closest body and strive to cause chaos. They gain the intellect of whatever beast they consume in this fashion, and usually drive them to their death in the demon’s ignorance on the need for sleep and sustenance.
Demons, as a rule, fear and flee the deaths of a great-souled individual. At the moment of death, each and every being is granted a personal miracle, where their god receives them and takes up their spirit to Their heaven. Those who turn from their god are sundered, forced to walk the world as a ghost that none can see or here, until they slowly fade away into nothingness. This death (no matter what path the being chose) opens up a fleeting gateway to the gods. If the individual is strong of will and can conquer the demon, this also provides a means by which it can be forced back to the Abyss.
A demon cannot willingly abandon its mount for another – it can, however, forcibly kill it in order to leap to whatever other life is nearby.