Demonology

Demonology is the study of demons or beliefs about demons.

See Wikipedia's entry on Demonology for more detailed information on its forms.

General traits of Demons in the Supernatural Verse

Appear as a ‘black smoke’ in incorporeal form
Presence may leave traces of sulfur
Manifest by possessing humans
Can resurrect people but only if a deal is made
- A possessed human will be unaffected by physical harm, until dispossessed
Exorcism will drive the demon from its human host and send it to hell
Have a range of abilities including mind control, telepathy, telekinesis and super strength
To date the only method of permanent dispatch is to shoot them with the Colt
Humans possessed by demons exhibit black, red or yellow eyes depending on the demon involved.

Eyes turn entirely black during possession, though this can seemingly be turned on and off.
They are impervious to hallowed ground ("that may work in the minor league, but not with me" - Meg, Salvation), but not to Holy Water
They can be exorcised and thus the demon returned to Hell
Possession can occur by physical contact
Restricted by the salt barrier
Vulnerable only to the Colt
Can resist exorcism Meg!Demon in 2.14 Born Under A Bad Sign
Can trap themselves within their human host using a binding spell
Can communicate
* via the Goblet of bloodwith Yellow-Eyed Demon
* via EVP 1.04 Phantom Traveler

deals with
- Robert Johnson in 2.08 Crossroad Blues in 1930
- George Darrow, Sean Boyden, Silvia Growman and Evan Hudson in 1996 in 2.08 Crossroad Blues
- Dean in 2.08 Crossroad Blues
- Dean in 2.22 All Hell Breaks Loose: Part Two

presence in an area will be presaged by cattle deaths, electrical storms and temperature fluctuations.
makes clocks stop, and electical devices go haywire
is impervious to Holy Water
has yellow eyes (iris and pupil)
Impervious to the salt barrier
vulnerable to the Colt

Meg Masters refers to the Yellow-Eyed Demon as "Father" in 1.11 Scarecrow
In 1.22 Devil's Trap, the Yellow-Eyed Demon refers to Meg as his daughter, and Tom as his son.

Acheri Demon: summoned by Ava in 2.21 All Hell Breaks Loose: Part One. Sam says they manifest as children. He dispels it using an iron road. It cannot cross a salt barrier.