Angels were introduced to Supernatural in season four. It made sense, of course — demons were a thing in this universe already, so why not angels too? Dean Winchester, in particular, had a hard time believing in the existence of angels though, and it took him quite a while to warm up to the idea despite angels being portrayed as… well, angelic, in culture. And rightly so.
Angels have proven they can be extremely corrupt and aren’t the sweet guardians of humans that religion and other media has made them out to be. Lucky for the Winchesters though, there are a few weaknesses they have.
The angel banishing sigil has made for some pretty cool scenes in the show. What happens is, the sigil is drawn in fresh blood (and yes, it must be blood) and when it’s hit, it banishes all angels from the area. This often comes in useful for the Winchesters, who sometimes need a quick head start on the angels hunting them.
It should be noted that angels too can use this spell, and aren’t banished if they’re the one using the sigil. For example, Castiel actually draws the sigil on his own chest at one point to banish angels, which is a really brave move. That had to hurt.
When Uriel tries to kill Castiel, we find out that there are blades who can kill angels. Although most angels seem to carry these blades, it turns out that demons can too. Meg, in particular, seems fond of carrying one, but Abaddon and Crowley can also be spotted with one at points. Since it seems like the quickest and more surefire way to kill an angel, it’s understandable the demons would want to get their hands on one too.
It’s a long dagger that can also be used to kill demons, hellhounds, and a whole variety of creatures; which makes total sense, if it’s strong enough to instantly take down a creature as powerful as an angel.
The angel depowering spell was introduced later in the series and hasn’t been used very much since it seems to be pretty complicated. Metatron, however, uses it on Castiel, which is its first appearance in the show.
It takes a lot of blood because many of the Enochian symbols must be drawn in said blood. They have to be written in a very specific manner and when the last one is written, it will ignite the spell and disable any angel in the area.
It seems like a lot of hassle to go through for one angel, but if there were a large group of them, it’d probably come in handy.
Before Supernatural, many people thought that only demons and the devil had to be exorcised from humans, but the show revealed that this isn’t true in its lore! Angels need vessels as much as anyone else. Look at Castiel, who’s been using Jimmy Novak as a vessel for… well, forever. Guess the show can’t quite let go of Misha Collins. Poor Jimmy.
Like demons, they can be released from their vessel via exorcism. Once they’re in one, it isn’t a surefire thing. The vessel may not survive this though, since having an angel inside of them is… well, a lot. Sometimes it isn’t worth doing at all if the main goal is to save the human.
Although this specific pattern of sigils has no name, they can be used as concealment from angels when carved on the ribcage. This has to hurt but it's apparently worth it. Sam uses the sigils on his ribcage to hide from even Lucifer, who comes to him in a dream to tell him he’s a hard one to find. If even the Archangel can’t find Sam, these sigils must work.
It’s Castiel that has to carve them onto Dean and Sam, of course, through some sort of angel magic. Actually opening them up and carving sigils into their ribcages would probably be really dangerous otherwise.
An angel trapped in a ring of holy fire cannot escape from it. They could literally be trapped there forever.
It’s a hard one to pull off, though. Angels aren’t stupid, so to bring them into a ring of holy fire takes a lot of skill and perhaps some trust on the part of the angel. Sam and Dean manage to do it to Gabriel though—and also to Castiel later on—although this is mostly because Castiel trusted them and wasn’t expecting them to trap them.
It’s a unique angel prison, but the moment the holy fire is rained on or put out, they can escape. So it’s good for a short line of questioning, or in a very dry place since the angel can’t put it out themselves.
The deepest part of Hell holds Lucifer’s cage, where even archangels can be held without fear of them escaping. It does have multiple entrances, strangely enough, but it seems to be very heavily protected; Castiel says it’s more guarded than where Dean was in Hell, and pretty much impossible to get to and open. Though he does manage it to rescue Sam.
Where it actually exists doesn’t seem to be certain. It can be accessed from any place, which suggests it might actually be on another dimension; as all of Hell seems to be. Regardless, it’s the best prison in the show and is very effective at holding anyone — even someone as powerful as Lucifer or Michael.
It's the seal used to lock away the darkness. God gave it to Lucifer, who then gave it to Cain, and it was used as the source of the First Blade’s power. It’s an extremely powerful weapon that can even corrupt angels, and is nicknamed “the first curse.”
It does grant someone a lot of powers, as we see with Dean, but it also corrupts them far too much and makes them desperate to hold onto that power. The lesson to be learned with the mark is that it doesn’t matter how awesome it makes a person; it’s simply not worth it at all.
A little weaker than some of the other weapons that can be used against angels, but pretty effective in an emergency, are hex bags. They’re created by witches and often used for spells but if a person is carrying them, they can hide from demons and angels — which would come in hand in the Supernatural world.
Well, mostly, anyway. An Archangel seems powerful enough to be able to override a hex bag so if you were looking to outrun one of those, best get carving those Enochian symbols onto your ribcage. For the lesser angels and the demons though, these are pretty ideal. And less painful to get.
Eve escaped purgatory and, rather than being the sweet biblical figure we think of, was an absolute monster. She was called Mother of All and seemed to be even more ancient and powerful than the angels. In fact, she could suppress the angels’ powers just by being in their presence, which is something no one else has been able to do.
She’s been around for longer than angels have, and although we don’t see her killing one, it’s easy to assume that she would be able to if she were to try. Except maybe the archangels, the only creature she doesn’t predate.