Demons

THE EYES:
One Black and one Greyish Eye: Lower than Black eyed, Specifically is the Acheri Demon which appears as a little girl and often makes children sick. This is one of the very few who can appear in their original forms/without possessing anyone.
Black: Regular Demon
Red: Crossroads Demon (Makes deals with people)
Yellow: Demon Army General
White: Knights of Hell (Handpicked by the fallen angel Lucifer to become demons)
Grey/Off-White: Demon of Halloween

Universes: Supernatural

Special Abilities:
Lower-hierarchy powers
Telepathy and telekinesis - Demons can read minds. Some can influence an object's movement with their minds.
Superhuman strength and enhanced endurance - While hosting a demonic entity, a human's body can be made to perform extraordinary feats and resist damage. However, when the demon leaves, the host often dies of its injuries.
Seeing reapers - Like angels, demons can perceive entities that are invisible to human beings, like reapers.
Can resurrect or heal people, but only if a deal is made.
Capable of overpowering Alphas; a group of demons captured the Alpha Vampire on Crowley's orders, though only after it had been injected with enough dead man's blood to bring down a nest of regular vampires, and when they all attacked at once.

Upper-hierarchy powers
Mind control - Demons can influence and control the actions of human beings.
Pyrokinesis (known: Azazel, Brady; shown: Crowley)
Injury to humans by thought (shown: Azazel)
Destruction of objects with telekinesis (shown: Crowley destroys a light) and with the "fiery white light" (shown: Lilith, Samhain)
Overpowering or possessing reapers (overpowering: Alastair, possessing: Azazel)
Resurrecting people at will (Crowley, claimed).
The ability to exorcise and send lower-tier demons back to Hell with a single touch. (Abaddon)
Smiting other demons with a touch. (Cain)
Ability to partially enter a human's body to extract information (Abaddon)
While in Hell turning demons to dust with a snap of their fingers (Crowley)

Origin: Lucifer when he tried to go after god, god dropped him from heaven. Lucifer found Lilith and stripped her of her humanity, turning her into the first demon.  

How Do You Become one:
All demons were once humans. The first was Lilith. Lucifer stripped away her humanity and turned her into a demon. In order for someone to become human, they must end up in hell and have their humanity taken away. 

Weaknesses:
Preventing possession and location:
Exorcism - When a demon is exorcised via ritual, it returns to Hell.
Preventative Charms - After Sam is possessed, Bobby gives the boys charms to protect against possession.[5]
Preventative symbol tattoos - Sam and Dean reveal that they have the protection symbol tattooed on their chests.[9]
Hex bags - Hex bags can be used to help disguise and hide a person’s whereabouts from demons.[9]

Hindering Demons:
Holy water - While most have some vulnerability to holy water, higher level demons, such as Lilith and Azazel, appear immune.
Consecrated ground - Some demons are able to enter consecrated ground such as churches, as shown by:
Meg in 1.21 Salvation
Father Gil in 3.04 Sin City
Alastair and Ruby in 4.09 I Know What You Did Last Summer
Azazel in the flashback scene in 4.22 Lucifer Rising
Lilith and Ruby in the present in 4.22 Lucifer Rising
Crowley and the demon possessing Channing in 8.01 We Need to Talk About Kevin
Crowley and Abaddon in 8.23 Sacrifice
Abaddon, Sister Agnes and two other demons in 9.17 Mother's Little Helper
Salt - Most cannot cross a line of salt and they feel intense pain when they come in contact with it. Hunters use it in shotguns to wound them.
Iron - They cannot cross an iron line, and can be hurt with an iron rod.
Palo Santo - Burns in a similar way to holy water.
Devil's trap - A symbol that is marked on the floor or ceiling that can trap a demon within it. If carved into a bullet and shot into a demon, it will bind the demon to their meatsuit and make it impossible for them to move far.
Holy fire - While not capable of killing a demon, it will cause them great pain as shown when Meg was tossed into a ring of it by Castiel to act as a bridge out and when Sam doused Abaddon in it causing her so much pain she fled her meatsuit.

Means of Killing Demons:
The Colt - Until season three, the only method of permanent dispatch was to shoot them with the Colt and one of the original bullets. Bobby rebuilds the Colt with Ruby's help so that it can kill demons with new ammunition.[1]
Ancient demon-killing knives of the Kurds - Ruby had a knife that can kill demons.[10] It was later revealed that this knife is one of the demon-killing knives made by the Kurds.[11]
Angels - Angels have the power to kill demons with a touch.[4][12]
Sam's powers - Late in season four, Sam's powers also allow him to kill demons.[13][14]
Death's scythe: It is mentioned multiple times that Death's scythe can also kill demons.
Burning earthly remains - Demons, like spirits, can be killed by burning the bones of the bodies they had as humans, before they became demons.[15]
Spells - According to Ruby, there is a spell that can kill every demon in a one-mile radius; as long as the meatsuits haven't been killed already, they will survive the spell. The spell was never seen used, but it is known to require the heart of a virgin to work.[9] Demons can also be killed by a spell described in the Word of God tablet that completely destroys both the demon and the meatsuit. Kevin Tran and his mother refer to this spell as a "demon bomb" and it requires ingredients from all over the world. According to Kevin, just the first three ingredients are nearly impossible to get.[16][17][18] Crowley's mother, the witch Rowena, invented yet another spell that kills demons and apparently their meatsuits as well. This spell requires a Hex Bag be held by the demon as the witch recites the incantation.[19]
Angel blade - An angel's blade is also capable of killing demons.
Angel sword - As the sword version of an angel blade, it can presumably kill demons.
The First Blade - The First Blade, combined with the power of the Mark of Cain, can kill any demon, including the Knights of Hell. The First Blade is the only known weapon capable of killing a Knight of Hell.

Strengths: *See abilities*

Food Source: Do not need to feed on anything, though they are often after souls.

Forms: A few can use their regular forms, some need to possess people in order to survive on the surface.