One monster in Supernatural that’s been present for most of the series is demonkind. The demons of Hell have forever been gracing Earth in this series - in fact, one is in the very first episode, since it’s the one who killed Mary Winchester.
It’s an old horror movie trope that’s easy to play on because demons themselves are a frightening thought, but it’s one that Supernatural has played on pretty well and expanded their lore to be enormous. In fact, they have a comprehensive list of weaknesses for these demons - lucky for the Winchesters, who’ve had to employ each of them on more than one occasion.
10 Devil’s Trap
A Devil’s Trap can be drawn on the floor or ceiling and if a demon can be tricked into stepping inside of it, they’re trapped there. It doesn’t hurt or kill them, but it does hold them in place and has allowed the Winchesters to question demons or perform an exorcism and set their vessel free. Pretty convenient, when a demon could otherwise just interrupt an exorcism by taking off if they weren’t stuck in place.
It’s an old classic, a weakness that was used in one of the earlier seasons and has been utilized time and time again. You’d think the demons would become wise to this and stay away from concealed ceilings or floors…
9 Holy Water
Holy water is a common trope often used in other media as something that hurts demons, and it’s no different here. The water burns them and can be used as a means to stun or harm there. It can even be used as a means to detect if a demon is present inside of someone, since it can be handed over and disguised as normal water; a demon is put in such agony if they touch holy water that they’re completely unable to smile through the pain and pretend everything is normal. Which is pretty lucky for the Winchester brothers.
Another trope often used in other forms of media when it comes to demons: exorcisms. Exorcisms are used to expel a demon from a vessel’s body and set them free. Assuming said vessel isn’t too damaged: if the demon was operating in a fatally wounded body, then the person will not survive once they leave.
But assuming they can be trapped and expelled without the person being too badly injured, they’ll survive. They just might be extremely traumatized by the experience. The demon is expelled in a cloud of black smoke and sent straight back to Hell, where it belongs.
7 Anti-Possession Sigil
The Winchesters have this sigil tattooed on their chests, usually concealed beneath their shirts. It’s pretty much a must for any demon hunter.
When the sigil is present on someone, they officially can’t be possessed by a demon. It may not last forever though - if the tattoo is slashed or cut in some way and the sigil is broken, a demon can then possess that person. So the people who have these might want to protect that area of their body with their life when in a fight, particularly with a demon. It would take the demon less than two seconds to jump right on in there after the sigil was broken.
6 Hex Bags
Hex bags are created by witches and used for their spells. They contain a lot of ingredients and have multiple uses, but one of the handiest is that they can conceal someone from demons if they carry one.
It doesn’t just work on demons too. The hex bags can conceal a person from hellhounds and even angels. Archangels are above them, but it seems as though the hex bags may just work on any demon, and that’s reason enough to carry them. One of the most surefire ways to stop yourself from being hunted by one of these awful creatures.
Much like holy water, this seems to burn demons. Iron, in the series, has a lot of supernatural properties and is not only used to defend hunters and victims, but can actually be used to defeat other creatures. Even ghosts and hellhounds are vulnerable to iron.
The problem is that high-level demons are unaffected to the point that iron has no real use against them. When it comes to low-level demons though, much like holy water, they’ll be affected to the point that they can’t hide it. The Winchesters will touch someone with iron to see if it might be a demon in disguise and if it’s a low level one, they’ll find out immediately.
4 Holy Fire
Holy fire is another weakness that both the angels and demons have in common. It can be used to destroy a demon’s vessel, so should probably only be used in dire circumstances. After all, the vessel is usually innocent and it’s the demon doing all the dirty work!
But sometimes a vessel is necessary collateral and can’t be saved, so in those cases…
It will either expel the demon or, in the case of low-level demons, will actually kill them, so it’s a pretty powerful substance against these monsters. Sorry to all the vessels who’ve been destroyed by it…
3 Hallowed Ground
Another weakness of low-level demons only is hallowed ground. Like in a lot of other media, demons can’t set foot on it. The Princes of Hell can though, so the stronger the demon, the less likely this is to work.
Samuel Colt very smartly had five churches built on the points of his huge Devil’s Trap, which was a worthwhile investment to stop demons coming close. Ghosts can enter hallowed ground though, but doing so will destroy them, so that’s another added bonus.
Hallowed ground is featured very frequently, from the first season all the way up to the most recent ones, so it plays a pretty big part.
Salt is one of the weapons against a demon that we see used very early on in the show, and it continues to be used - against not just demons, but ghosts and hellhounds too.
It can be loaded into a gun and shot at demons. It can also stop demons from entering a room if a line of salt is placed at the doorway, since they apparently can’t even step over it. At its worst use, it can be poured down a demon’s throat and used as a form of torture, as Dean demonstrates. In extreme cases, it forces a demon to vacate its vessel, since it probably can’t stand the pain any longer.
“Christo” means relating to Christ, to it makes sense that this a weakness of demons in the Supernatural world.
It’s also the thing we see used in the early seasons, although Sam and Dean sort of… seem to forget this is a thing in the later ones. When they say this, it doesn’t hurt or kill the demon, but it does force the demon to reveal their black eyes. It was very handy for them when they weren’t quite sure if someone was possessed, as they could slip this into the conversation and get either a weirded out look in response or an angry demon flashing its black eyes because it’s been caught.