Catching up on this week's episode of the revamped Charmed (which I'm loving) this morning, the combination of demon powers and smoke got me thinking not just about the original Charmed, but also Supernatural (the mother of all demon-smoke shows).
Where did this smoke-as-demon's-incorporeal-form concept originate?
Is there a "real world" precedent in ancient demonology texts for this or is it simply a televisual conceit because it looks cool?
And if so, does it require any rules mechanism or is it simply a method of travel?
[Actual 'possession' of a host is a different matter and clearly requires mechanics, especially when player-characters are involved as either the targets of possession or the priests trying to use the power of their god to compel the demon out!]
The idea of demon's smoky ethereal forms is one I've long held in reserve, but never been in a position to employ at the table.
I've always had in my mind that demons have three forms: their natural body that they wear in Hell (or wherever they reside), which is the traditional horns, spikes, cloven hoofs etc; a human form, which is the flesh suit they 'put on' when they come to Earth; and their smoke form for transiting out of Hell and between possessed bodies.
One day, I'll run a game where the player-characters are having to tackle these demons...