Demon Smoke

Demons appear as smoke in their incorporeal form; they manifest by possessing humans, alive or recently deceased, via demonic possession. Acheri demons are the only exception, as they are able to manifest from their smoke form into that of a little girl. When an exorcism is performed, this forces the demon to leave its vessel or meatsuit, and the smoke is usually seen pouring out of the person's mouth. In nearly all cases the smoke is black, although Crowley's smoke was shown to be red..

Abaddon possesses the ability to partially enter a person, by sending a piece of her "smoke" form into the person's body, to read their thoughts.

Episodes

1.04 Phantom Traveler

An unnamed demon with an affinity for causing disasters begins possessing people and causing commercial airliners to crash. This demon shows different attributes than demons that would be seen later, for instance: appearing as more of a cloud of dust than smoke, having the ability to enter a person through their eyes, and violently reacting to the word "Christo."

1.22 Devil's Trap

After luring Meg into a devil's trap in Bobby's home, Sam and Dean try to get information out of her regarding the whereabouts of John. When it becomes clear that Meg is not going to be forthcoming with them, they threaten an exorcism, which gets her to finally give up all she knows. Satisfied that she is telling the truth, Dean orders Sam to finish the exorcism, much to Meg's displeasure. Though Bobby warns them that doing so will kill the girl being possessed, Dean justifies it as putting her out of her misery. As Sam finishes the exorcism, Meg throws her head back and screams, the demon leaving through her mouth in a black cloud of smoke and spreading out within the devil's trap in the ceiling before disappearing.

After Sam shoots an Azazel-possessed John in the leg, John begins pleading and ordering Sam to finish the job while he is still in control, much to Dean's protest. Before Sam can make a choice, Azazel smokes out of John's body and escapes through the floorboards of the shack.

2.01 In My Time of Dying

After the Impala is run off the road, the demon steps out of the semi-truck and rips off the door of the Impala, only to be met with Sam pointing the Colt at it. The demon tells Sam that he is bluffing, but when Sam cocks back the hammer on the Colt, it is enough for the demon to exit its meatsuit and make its escape into the night

2.14 Born Under a Bad Sign

After suspecting something isn't right with Sam, Bobby secretly doses a beer with holy water, revealing that Sam has been possessed by a demon, and knocks him out. Sam wakes up tied to a chair under a devil's trap, where Bobby begins reciting an exorcism while Dean taunts the demon. After the demon fails to smoke out, they learn that it has branded Sam with a binding link, preventing any expulsion from his body. The demon then uses terrakinesis to cause a crack in the devil's trap, freeing it to assault Dean and Bobby, and revealing itself to be Meg in the process. As Meg is about to deliver a killing blow to Dean, Bobby grabs Sam's arm and burns the binding link, which sends Meg retreating up the fire place in smoke form.

2.21 All Hell Breaks Loose: Part One

An Acheri demon appears before Jake Talley when he notices a young girl standing at a window in a schoolhouse; as it is about to attack Jake, Sam dispels her with an iron rod. When Ava seemingly goes missing, and Sam and Jake set out to search for her, she approaches Andy Gallagher and proceeds to summon the Acheri. A cloud of black demon smoke appears outside the window, and as Ava has broken the salt line, the Acheri is able to enter the room. Once inside, the Acheri manifests as a young girl and knocks Andy down. It wastes no time in killing him; Andy screams in pain, his blood splattering everywhere, until he is dead. Ava watches his corpse for a second, amused, then begins screaming. When Sam arrives to see what happened, he is quickly able to see through Ava's manipulations, and as Ava attempts to distract Sam with talking, the cloud of black smoke returns to the window. Just as it is about to enter, Jake comes from behind Ava and twists her neck, killing her instantly, causing the demonic smoke to retreat and disappear.

2.22 All Hell Breaks Loose: Part Two

With Jake having embraced his psychic powers after giving in to Azazel for his family's safety, he takes the Colt and places it in the Devil's Gate, releasing hundreds of demons and spirits from Hell into the world before Bobby and Ellen can close the gate.

As Azazel stands before Dean, prepared to kill him, the spirit of John Winchester appears behind him and rips out the demon smoke from Azazel's meatsuit and holds on to him. When Azazel is able to wrestle free from John's grip, he quickly smokes back into his body. The distraction proves fatal for Azazel, as it grants Dean enough time to pick up the Colt and shoot the demon in the heart, killing him once and for all.

3.01 The Magnificent Seven

Walter Rosen exits the house to take out the garbage. As he walks back to the house, the garbage cans rattle. He stares, walking cautiously towards them. They continue to rattle; he looks up and sees a demonic cloud swirling over the Chicago skyline in the distance. Panicked, he runs back towards the house, but trips before he gets there. A tendril of demon smoke pours into his mouth. The demon Envy stands in its new meatsuit, looking towards the rest of the demonic cloud now streaming towards Chicago, and smiles.

3.12 Jus in Bello

Waiting in their holding cell, Sam and Dean are approached by FBI Deputy Director Steven Groves, who cordially greets the Winchesters before shooting Dean in his left shoulder. Sam jumps up and grapples with Groves through the bars; Groves fires several more shots, narrowly missing Dean. While continuing to struggle with Sam, Groves' eyes turn black, prompting Sam to begin an exorcism ritual. Not wishing to be exorcised, the demon leaves Groves' body, disappearing into the ceiling air vent.

Later, Sheriff Melvin Dodd unlocks the cell, telling Victor Henriksen they are going to make a run for it to a SWAT facility in Boulder. Henriksen enters the cell and shots Sheriff Dodd in the head. Sam and Dean grab Henriksen, and shove his head in the toilet, which has been turned into holy water, and begin an exorcism. As Deputy Phil Amici runs in, Dean grabs Henriksen's gun and tells him to stay back as Henriksen lifts his head up out of the water, burning and screaming. Sam shoves him back into the toilet bowl and continues the exorcism. The demon pulls itself out of the toilet bowl one last time to tell the Winchesters "They're already coming." Sam shoves him back into the water and finishes the exorcism; black smoke shoots out of his mouth and up to the air vent in the ceiling.

Needing to retrieve supplies from the Impala, Dean ventures to the impound lot. As he starts putting things into a bag, the lights at a gas station flicker and thick black smoke with blue lightning races past. Dean quickly fills his bag and turns to see the black smoke coming towards him. As Dean runs back to the station, Sam is drawing a devil's trap on the floor while the others line the windows with salt. Dean rushes inside, warning the others of the demons that are coming. The demon smoke hits the building and surrounds the windows, engulfing the building and causing it to shake before it seems to disappear and all becomes quiet again.

After finding that the demons having taken meatsuits, Sam and Dean formulate a mass exorcism plan. The group all break the salt lines and devil's traps protecting the doors, allowing the demons to run inside and fight with Sam, Dean, and Henriksen, who lure them into the main office. With the demons in place, Dean tells Henriksen to play the exorcism recording. As the exorcism airs over the loudspeakers, demons flail and scream and pound against the outside doors, trying to get out. Black smoke begins to pour from the demons’ mouths. The bodies of the possessed people fall to the ground as the smoke swirls around the ceiling. There is an explosion of light on the ceiling, then everything goes still. The people who had been possessed start to get up as the electricity flickers back on.

3.16 No Rest for the Wicked

After siccing a hellhound on Dean and killing him, Lilith, in Ruby's meatsuit, approaches a pinned-down Sam and attempts to use her white light against him. To her shock, Sam survives without a scratch. He picks up Ruby's knife and begins to approach Lilith, who fearfully begins to back away before smoking out of Ruby's body.