SCP-682 in a nutshell. Its ability to spontaneously evolve and regenerate lets it counter, or at least survive, everything thrown at it. This includes SCPs that have reality warping powers. The Foundation's attempts to kill it are numerous and their failures often spectacular.
SCP-1633 adapts its strategies to the people playing it. Literally to the people playing it. After having deduced the player's strategy, it deduces that there's a player and shifts its attacks to them instead of the avatar.
Adult Fear: All of the SCPs are purely fictional, because there is no reason for the Foundation to contain anything "mundane" (for most of the time anyway). However, some SCPs do involve entirely possible scenario. Sure, a cyborg girl isn't real, but before that she was just a normal girl, abducted by a madman. Procedure 110-Montauk is something horrendous done to a minor who, before falling into Foundation hands, was kidnapped and horrendously abused by a Satanic sex cult.
Alien Lunch: Well, more like Alien Snack, but SCP-261 dispenses some truly weird items which may or may not be able to be described as "food". One example of "food" is the package of "Lemon Clams": a self-steaming package of clams, which, when eaten, taste vaguely of lemon. The problem? In-depth analysis of the clams do not match any known species of clam found on Earth.
Another fun example of "food" is the can of "SCREAMING [untranslatable]", which, when opened, did indeed scream very loudly (about 125 dB, which is the level at which pain and temporary hearing loss begin). Strangely enough, when the screaming stopped, the person holding the can stated that he was oddly full and did not need to eat for the rest of the day.
Heavily implied by The Administrator's letter, which claims that the SCPs themselves are the universe's conservation of insanity after the end of myths.
More particularly, several of the SCPs are implied to be the cause of certain Real Life myths themselves. For example, the file for SCP-953 notes that the people in the cultures it is traditionally associated with have had generations to learn to deal with it, and that their myths about the creature can be considered a crude precursor for formal Special Containment Procedures. Thus the surrounding folklore is one of the first things that should be considered when planning containment. There are several SCPs that are mythological beings, creatures, locations, or figures - Valhalla Gate pulls people from, well, Valhalla to do battle with the living, a kumiho, Jormungand, and Baba Yaga are in containment, djinn of all sorts are referenced...
One of the proposals for SCP-001 is a sheaf of papers that contains a complete, accurate report about an SCP. The problem is it's the next one to be found.
Almighty Janitor: Wilhelm Grungkok. He knows about the Foundation way more than one would expect from, well, a janitor, because researchers usually ask him to clean up their messy offices, leaving him alone with sensitive documents for hours. Oh, and he cleans up 682's pen on a daily basis.
The physically-invulnerable SCP-723-D's initial fate; sealed within a massive block of concrete. Given how badly written he was, though, it wasn't undeserved. He did manage to escape one last time, but the two thankless personnel tasked with his decommision killed him by complete accident, after SCP-723 fell victim to a previously unknown peanut allergy while the three were getting drunk at a local bar. They then put SCP-723's body back in the concrete. Just to be safe.
SCP-515 has to be restrained to the point of nigh-immobility, with his limb bones broken for good measure, because whenever 515 moves, a cluster of asteroids comes closer to Earth. The faster he moves (or, formerly, she, but the first 515 died and the current one popped up to replace her), the faster the rocks move.
SCP-747 is a group of children in animal masks that dance around any subject they take interest in, turning that subject into a doll over a period of time. During that period, the subject loses all five major senses until final transformation.
SCP-231 also has to be restrained at all times, and attended by doctors who haven't taken the Hippocratic Oath. Once a day, she has to be subjected to Procedure 110-Montauk, which is so horrible that most of the details are classified, or else she gives birth to something that will possibly end the world. Worse, the psychological trauma appears to be an important part of the process; after every fourth procedure, they erase her memory of the whole shebang so that she doesn't get used to it.
SCP-138, The Ever-Living Man. A severely decayed, hideously decrepit man who is at least 4000 years old, with dozens of unhealed mortal wounds all over his body, who for some reason cannot die... no matter how much he wants to. The SCP are trying to euthanize him, but so far, their attempts have been ineffective.
Victims of SCP-318 are imprisoned within paper scrolls, and they can only see and communicate with the outside world when unrolled (and the Foundation doesn't do that often.) If the paper is damaged enough, they stop responding... but it's unknown if they die, or just lose their only connection with the world.
Anyone who touches SCP-911 ends up floating in an infinite featureless void, unless they manage to escape through a portal that only opens rarely for a few seconds.
SCP-373 allows one to talk to people who, apparently, are imprisoned in a black void where they perceive nothing but the voice of whoever is talking to them. Though it might all be a hoax on part of SCP-373.
SCP-762 is an iron maiden that gives anyone inside of it a Healing Factor and immortality until they are released, but puts sharp spikes through their body. When it was recovered, it contained someone who was probably stuck inside for centuries.
Each of the band members of SCP-332 seem to be aware of their surroundings, but something unseen controls their movement, making them stand still like a statue until they all play in unison, trampling over anyone nearby. For nearly 40 years, they have been in physical stasis, not aging, nor taking any wear and tear by standing in the same spot, and now the SCP Foundation has placed a tall concrete barrier around them. The agents, for some reason, chose to confiscate the whole band, members and all, rather than the instruments, which were hinted to be the source of that controlling force.
SCP-1922 reanimates an hour after dying of natural causes. During this period, he claims his consciousness is transferred to a human locus filled with body parts and waits there until he reanimates. His continuing peripheral vascular disease is making his limbs gangrenous and require amputation. He slowly went insane, screaming every time he reanimates now, and his requests to cremate his body are denied.
Anyone who looks at SCP-531 when the statue is not looking at another of its own kind will undergo a slow and painful transformation into another SCP-531. Once complete, their soul is forever trapped in the statue.
SCP-1288's dimension heard about our 2012 Mayan Apocalypse and decided they should get in on that. The "Wow" factor is from the giant Mayan pyramids (apparently nuclear power plants) at the center of every major city.
Applied Phlebotinum: Beryllium bronze pops up in a lot in articles, like 1564, 14271348, and 1216. The Foundation has even applied it to make Scranton Reality Anchors, which are used to counteract reality bending, and are crucial to the containment of SCP-2000.
April 1st of 2010 involved one (or more) of the mods going through and editing articles into a more humorous state. Details included replacing researcher's profile pictures, and the containment breach of a self-inserting SCP: adding "And Fred was there." to the end of Foundation Tales pages, and general editing of SCPs (Classification: SUPER KETER)
Darkblade was here.
April 1st of 2009 featured multiple image replacements on the most popular SCPs, including depicting 682 (the Hard-To-Destroy Reptile) as Barney, 076-2 (the official Mary Sue boundary line), and 173 (the statue that attacks when you're not watching it) as the Statue of Liberty. Also, the site WoobieCan of Sealed Evil, 231-7, was cured and set free, and in its test log 682 was killed by cutting it in half and letting the halves kill each other.
And 914, the only SCP to surpass the original in popularity, was erased and relabeled as, basically, "This is a picture of a box full of gears. Why on earth does everyone like it so much?"
In 2012, the "Groups of Interest" page got a makeover, with the Red Team as the GOC, Anonymous as "Nobody", and Drosselmyer as Dr. Wondertainment. Plus there was a slot added for the Shark Punching Centre. Other SCPs had their pictures changed to comedic images.
Furthermore, Darkblade (SCP-777-J) and a Self Insert named Fred went on an SCP hopping adventure while trying to beat each other up.
And Dr. Clef's Proposal (SCP-001) is Lilith for the moment.
2013 now has all of the pages rewritten to be DogFacts.
2014 turned the site into "Super Cute Pets", with SCP-173 and SCP-096 shown on the homepage as an adorable puppy and kitten, respectively. 231-7's entire page was also replaced with an adorable bunny.
"Object Class: Thaumiel". It was initially used in SCP-001 related tales and proposals, to indicate an SCP that has the potential to secure, contain or protect the world from SCP objects as a whole, being objects integral to the Foundation mission. The other alternate interpretation is to use it for "Super Keter" SCP's, although this isn't borne into any of the actual objects using Thaumiel, and would more likely end up being used by the recently introduced "Apollyon" class.
It is also used in SCP-2000, slightly extending the meaning of the object class to also include objects which can rebuild the world after an apocalyptic event..
SCP-2003 is a form of time travel that will let the Foundation see into the future destruction of humanity. This however, doesn't quite match the other Thaumiel objects.
SCP-2799 is effectively an anomalous object compass.
Arc Welding: SCP-2000. Basically, pretty much every named character on the site was somehow involved in it's containment/creation/operation, including Dr. Clef, Dr Gears and Dr. Bright, as well as lesser-known individuals such as Thaddeus Xyank, Lowell Piedmont and the highly obscure Dr. Zartion, who only appeared in one tale.
Armies Are Evil: The Pentagon manages to convince the Foundation into using SCP-076 against the Taliban. In so doing, they irritate it so much that the brief window they had into its mind - ie, that it would respect a Worthy Opponent - is forever closed, and its containment area had to activate its onsite warhead.
SCP-1765, three nigh-omnipotent entities who use the Foundation's personnel as guinea pigs for their sadistic experiments. The first forces them to permanently and frustratingly take measurements of an ever-changing plumbing system. The second puts them through a hellish obstacle course with fireballs and giant hammers squashing them. The third makes its subject...choose a flavor of ice cream. note It's not clear if the subject eats the ice cream, he's just told to pick between two flavors. Also the flavors can be anything from chocolate to "That Shoe You Always Liked" to "God's Wrath".
From SCP-1006, a Marxist collective of sentient spiders:
Once supplied a source of black ink and poster sheets, SCP-1006 will communicate with humans by creating signs written in English. These communications are largely centered around demands for the dismantling of western imperialism, a scathing critique of the bourgeoisie, and a request for less mosquito spraying in the surrounding area of the park.
-One (1) █████ cryotube -Three (3) sets of standard Foundation surgical equipment -█████ ███ █████████████ -Two (2) D-Class research cadavers -One (1) gasoline-powered generator -A variety of chemicals, including large quantities of tryptophan, phenylalanine, █████████ and tyrosine, among others -One (1) container of powdered coffee creamer
In Dr. Robinson's Statement, after viewing SCP-1981 in 1994, Ronald Reagan became erratic and ordered the killings of "a civil rights lawyer based out of Chicago, a 15-year-old high school student in Oslo, Norway, and the four-year-old daughter of a New York investment banker." Barack Obama, Anders Breivik, and Taylor Swift.
From SCP-1954: "Experimentation logs show that after no less than 20 successful attempts at homemaking tasks, the instructions turn into detailed rituals, some of which mirror those which first were recorded in ███ ██████; some have never been previously documented. Most of these rituals involve murder, cannibalization, sexual encounters, self mutilation, and canned vegetables."
"SCP-2085 and SCP-2085-A have been linked to numerous criminal operations occurring between 2010 and 2013, including smuggling, theft, kidnapping, extortion, possession of fissile materials, corporate sabotage, embezzlement, copyright infringement, piracy, possession of narcotics with intent to sell, and tax evasion."
One of the items retrieved from SCP-261, a magic vending machine, is a 2-ounce bottle of Mr. Mercer's Amazing Condiment, which makes everything it's used on taste delicious, including "wood, stone, sand, rotten meat, and brussels sprouts".
The Foundation covered up the disappearance of SCP-191 and her fellow test subjects by blaming a serial killer who had been recently caught. Than in order to make sure he couldn't compromise the lie, they killed him just before his court date.
Assimilation Backfire: An attempt to kill SCP-682 with SCP-1361 resulted in 1361 essentially becoming 682. Once it was killed, 682's skeleton was extracted and regenerated as normal.
Author Avatar: Many characters are named after the usernames of their real-life counterparts. The avatars and the authors are not always alike.
SCP-524, an Extreme Omnivore rabbit who is so extreme that his diet includes himself. When the only remaining parts of his body are parts that he can't reach with his mouth, his mouth flips inside out, swallowing himself whole in one final gulp. Half an hour later he'll re-appear, whole and unharmed.
Most competent Foundation personnel. For example, one of SCP-140's archeological digs went very, very wrong. The doctor in charge of the site sacrificed his life to stop whatever the Hell was in there.
Also even though it's not specifically the Bermuda Triangle,SCP-1372 has a similar description. Being a spacial anomaly, in the middle of the ocean, that boats and planes disappear when they go through. However they do sometimes come back, but that is not a good thing.
Berserk Button: Apparently, SCP-387 (a pile of sentient LEGO blocks) will do something extremely violent and unexpected when shown a pile of Megablocks.
Experiment 387-e: Once a normal community of 387 was constructed, a small mound of Megablocks (a common copy of Lego) was placed near the community. When this happened, everything constructed of 387 stopped moving, turned slowly towards the Megablocks and [EXPUNGED].
If you're planning on getting something from SCP-261, do not give it counterfeit yen. The only thing it'll give you is a bunch of lethally poisonous gummy candies shaped like hands Flipping the Bird. It also doesn't like it when you press the return coin button.
If SCP-184 is placed inside a structure, its interior will slowly expand. At first the additional space will just be copies of and minor variations of the original structure, but as it continues the additional rooms and hallways become stranger and stranger.
Inverted with SCP-1767, which causes any affected building to be smaller on the inside.
SCP-1992 ("Indecisive Mobile Home"). When a person enters and moves through SCP-1993, imperfect copies of the person are created and move through SCP-1993 as well. As they do so additional rooms are created inside SCP-1993, increasing its interior space.
Big Screwed-Up Family The Brights. Out of seven family members, four work for the Foundation, the father, Adam was a junior researcher who rose through the ranks and became an O5, the mother, Evelyn was a medical assistant (and is probably long dead at this point), the oldest child, Mikell, was an agent nicknamed "Cowboy," who eventually made it to O5 like his father, and Jack, who was a normal researcher until he died while in contact with SCP-963 and is now immortal by way of bodysurfing two are SCPs, Sarah, the youngest child, was stillborn, resurrected imperfectly, got picked up by the Foundation and made SCP-321, and Adam spent the rest of his life trying to get her out of the Foundation's custody, without success. TJ, the youngest son, has healing powers that have a rebound kind of effect on himself, and was the one to bring Sarah back. The process was extremely traumatizing, to the point that Jack brought him to the Foundation where he was made SCP-590 and deliberately given numerous mental afflictions to lower his mental state to that of a toddler's. Jack saw this as doing TJ a kindness, as now he was blissfully unaware of the trauma he had through before. and the only child not involved with the Foundation in any way is the second youngest, Claire, who is a member of the Serpent's Hand, and leads her own team within it known as the "Little Sisters." Considering the typical behavior of the most prominently featured member of this family, and it's pretty jarring to see all this tragedy behind the quirkiness.
There's an eighth family member. A little sister, introduced in the Man Who Wasn't There canon, who used to be part of the Serpents Hand, became the new Nobody. She was Unpersoned as a result.
Black and Grey Morality: Pretty much all SCPs that aren't trying to outright destroy the world or kill people are extremely dangerous. Take into account that there are other organizations that are trying to use SCPs for their own agendas and it's almost outright Black And Black Morality. The Foundation is a slightly Grey entity, and even then, they've slaughtered millions, altered reality, and are toying with forces they barely understand. But, like one short story says "You want happy endings? Fuck you. You're alive to read it. God help us all."
Although that example is a strange one, as the only thing being covered up in the source document is the precise nature of Dr. Clef himself, and that it's a fig-leaf coverup of another researcher's berserk moment.
Blessed with Suck: Name-checked in the talk page for SCP-2102: He should be a Super Soldier (he even gets an X-# designation) because of his invulnerability to radiation (possibly caused by exposure to said radiation) combined with an experimental fast-healing solution; instead the healing process is imperfect and in order to prevent his flesh from growing uncontrollably he's been a deaf, blind, mute, and paralyzed mass of cauterized scars in the shape of a human for 42 years.
Blue and Orange Morality: Many of the "Sentient" SCPs run of this, and even the more bloodthirsty SCPs could be argued are simply doing the things they do because they do not know any better.
Special note is SCP 049, who thinks he's curing people from a (non-existent) plague, by killing said people and turning them into zombies. From the doctor's perspective however, he is simply curing people.
One of the most notable examples, however, is SCP-835, a creature that is horribly disgusting in its own right, until you read the uncensoredlogs from the mission and discover that it is composed entirely of parts of the human anatomy. Tooth enamel, muscle. All from humans it has digested.
A more offbeat variant is SCP-524. It's a bunny rabbit that can eat anything. Including itself. It will regularly eat parts of itself, or even its whole body. Literally. It can eat its own head.
A lot of articles will read like this, with the article seemingly describing a normal person/object with mundane powers until you read the part about how it kills/mentally scars/otherwise ruins you. For example, a magic boarding pass that transforms into a valid ticket for the nearest public transportation vehicle, completely indistinguishable from any normal ticket (like the bus pass in your wallet right now). And then once you reach your destination, it erases you from existence.
Performance Incident #: 14 Performance: "Play With the Jenklsedn" by "Rodney Harper" Program Description: A play all children should attend, Play With the Jenklsedn addresses problems of growing up, family issues, and even how to deal with a family pet. Observations: Scenes include "Bad Words", "Why We Share", and "Sexual Problems with Cats".
One of the items dispensed from SCP-261 is a package of "Dimensional Donuts". These are small, edible donuts with a spacial anomaly where the hole would be. Things sometimes fall out of this "hole".
Item Description: Dimensional Donuts — A brightly colored box of donuts, labeling in Spanish. Donuts possess a small interdimensional anomaly, located in the hole of the donut which is destroyed once the ring of the donut is broken. When held sideways, small objects fall out of the hole, the object varying depending on person, donut, and time of day. Items noted include small candies, slices of fruit, jigsaw pieces, various forms of ammunition, blood, gasoline, various insects of unknown species, and human fingers.
SCP-1954, the 'Housewives Handbook' contains the following line about how the instructions go from weird but mundane (such as putting cat hair in meatballs) to insane rituals:
Most of these rituals involve murder, cannibalisation, sexual encounters, self mutilation, and canned vegetables.
In-universe, there is SCP-993, a children's' television show about "Bobble the Clown" which sends viewers over ten into a coma for the duration of the program. Like most children's' shows of the particular format, it has the normal sort of fourth-wall-breaking, speaking directly to the audience as he teaches the under-tens to commit any number of atrocities. More recently, it seems to have caught on to the SCP Foundation's efforts to keep it from being broadcast to the world; the two most recently archived episodes are Bobble Hates You. note Bobble the Clown sitting in a chair, glaring at the viewer for thirty minutes straight and (EXPLETIVE) YOU (EXPLETIVE) YOU (EXPLETIVE) YOU.note Bobble the Clown in the room where the Foundation has his show archived, angrily telling the viewer how to breach containment of several dangerous SCPs and murder several important Foundation personnel, featuring an appearance by the animated version of a researcher who happened to be passing by the archive at the time shown on the clock in the show.
Then there's S Andrew Swann's Proposal. In the end, it concludes with the basic truth of the matter: But we found out that there is a God, and it is SCP-001. And it’s a bunch of horror writers.
Brick Joke: In the experiment logs for SCP-261, a Running Gag is that all Dr. King can get out of it is apple seeds. Then later, in the experiment logs for SCP-294, Dr. King requests "a cup of room-temperature superconductor"... and gets a cup of apple juice with seeds floating in it.
And again in the experiment logs for SCP-978, Dr King's photo develops as...a closeup of an apple seed.
The Unusual Incidents Unit (UIU), an underfunded division of the FBI that is very inept compared to the other Groups of Interest and is continually used and manipulated by the Foundation.
SCP-3467-J, whose containment procedures include making fun of him at every waking moment.
Cain and Abel: There's a human SCP named Cain, and one named Able (with that spelling, though it used to be interchangeable). Cain is Able's Berserk Button (though Able is The Berserkeranyway.) Interestingly, Cain is a friendly, helpful guy whose unfortunate effect on plant life and soil is what makes him Euclid class (that's bad.) Able, on the other hand, is a Keter class (that's ultra-bad) unkillableAx-CrazyBlood Knight to the point of basically being a human version of good ol' 682. Looks like the good book didn't give us the whole story. They used to be more interconnected (it's implied they originated from the same place, and exposure to each other caused Cain to go into [DATA EXPUNGED]), but with Able's Re Tool, they're now separate, only bound by their names.
The stillborn child of Researcher Adam, he revived her using several SCPs, the result is SCP-321.
When a severed human head is placed into SCP-827, a living copy of the person the head belonged to was created, albeit with a flat head, malformed intestines, and communication consisting solely of writing the letter G.
Cameo: A couple of the joke SCPs - and a few of the regular ones as well.
Big Biblical names, Strega Nona's pot, The Little Mermaid, Halloween, Santa Claus...
Canon: Loose, and kept that way. In theory, "there is no canon". Any work on the site is allowed to ignore or contradict any other work on the site, and every person's headcanon is valid. In practice, any work that violates too many people's headcanons gets downvoted enough to be deleted, turning Fanon Discontinuity into Canon Discontinuity.
Cannon Fodder: Dying is literally in the job description of Class D Personnel. It can get quite blatant; for instance SCP-120 notes that a moon base was constructed after expending "vast amounts of money and D-personnel".
Despite being Elite Mooks, the Foundation's Mobile Task Forces are surprisingly easily defeated. (Given the nature of what they're up against, this isn't entirely surprising. Even the SCPs that aren't actively hostile are often very difficult to handle.) Read through any given incident report featuring any given Mobile Task Force and watch the team quickly fall apart, one member at a time. Yes, even that time they went after a non-sentient SCP whose only known ability was to produce an infinite amount of pasta.
MD: This is MD, we're on floor seventeen, ME is down! L1: Down? Why? MF: Some farfalle cut him to death, fuck if I know!
Of course, this depends on SCP to SCP. Some have managed to destroy horrible magic artifacts with nothing but modern day weaponry.
It might help if you know where D-Class personnel come from. Most of them are prisoners taken from death row, on the basis that since they're going to die and are no longer afforded any human rights whatsoever, we might as well throw them at anything that we can't get volunteers for. A few of them are instead ex-members of Foundation staff, who got busted down to D-Class after they misbehaved so badly that they may well have endangered their entire facility for a petty lark. Either way, any D-Class personnel who manage to survive testing by the end of the month are executed.
Cats Are Mean: SCP-511; a living, cat-shaped mass of debris, flesh, and rot. It's always surrounded by hordes of cats, and makes them very unpleasant. 511s are made by the cats. The cats made it because they hate us.
SCP-607 is a cat that is bonded to somebody it declares to be its owner in a way that causes the owner to suffer any injury it does. The cat will regenerate or revive after any sort of injury. The owner, however, will not, which is bad since the cat is actively suicidal.
Subverted with SCP-529 (a.k.a. "Josie"), who is quite affectionate despite not having any hindquarters to speak of.
Caustic Critic: SCP-1722 is a walking stick with the soul of one that usually criticizes any form of recorded media within a five meter radius by inserting commentary on it.
Censored for Comedy: In the more comedic entries, expletives are censored with [EXPLETIVE REDACTED], and sometimes simply [REDACTED] or [DATA EXPUNGED].
Cessation of Existence / The Nothing After Death: SCP-2718 subverts it: A resurrected O5 declares that after he died there was nothing... for about a day, then his consciousness went back into his body and felt every excruciating moment of his body decomposing and being spread out and eaten by wildlife while feeling as if he were holding his breath "beyond bearing". He was the only O5 who hadn't "enhanced" his lifespan with SCPs so when he told the rest of the O5 Council why he was suddenly so concerned about his and even the D-classes' health they believed him and completely freaked out—
"We must declare human death a Keter SCP," [O5-8] demanded, "and contain it at any cost."
—until O5-1 told everyone to shut up and flooded the council room with amnestic gas.
Addendum 076-08: As of 08/11/????, SCP-076-2's weapons have become noticeably different, being constructed of an unknown dull, dark brown metal, the items mechanical in design and nature, rather than traditionalist iron forged items. Rotating blades, chain edges, and drills are often present on subject's weaponry, powered and operated by unknown sources. It is unknown as to what prompted this change, and SCP-076-2 again refuses to divulge any information regarding it, stating only "Your people have created such odd blades. I thought I might see how they worked."
Clef recounts a time when he was bringing a chainsaw to work to test if it had any anomalies worth researching, but wound up in the middle of what he thought was D-Class riot (but was actually a costume party for the research staff). Half the research staff died that night, and the chainsaw was discovered to be just a regular chainsaw after all.
Children Are Innocent: Played with. While there are child SCP items (many of which are creepy), very few of them are actually hostile or malevolent and even the ones that are hostile/malevolent are (most of the time) not so of their own volition but because they've been altered or brainwashed or are being manipulated by an outside force.
He handed me a pair of field glasses. Take a look, he said. I saw the German missing half of his head, still screaming. ... The Frenchman, in his terrible calm voice, explained that his shot had to have destroyed at least a quarter of the soldier's brain tissue. Enough to cause instant death, he said. But watch. I kept watching through the field glasses. The German didn't stop screaming... the Frenchman lined up another shot. The rest of the soldier's head was now gone, and the screaming was replaced by some sort of low grunting, the likes of which I have never heard from men.
Circle of Standing Stones: SCP-526 "Valhalla Gate" is a ring of nine rune-covered standing stones on a hill in Norway. Each morning at sunrise a group of what appear to Einheriar (spirits of fallen warriors, from Norse Mythology) appear on the hill and either dig in or move off the hill and attack anyone they find.
Opening Night: Not an eye sees our caravan pull up in the moonlit lot. Not a soul hears the sound of our spikes driven into the earth. One day we're not there, the next day we are.
Which is itself a horror version/shout out to The Night Circus, which literally begins with the line "The circus arrives without warning."
Clap Your Hands If You Believe: Believing you can keep SCP-616-1 open will make you able to keep it open. For this reason, the Foundation painted Satanic symbols all over it and manned SCP-616 flights with devout people.
SCP-239 is a Reality Warper who doesn't fully understand the nature of her powers. Instead, what she believes to be true becomes true. People are exceptionally nice to her because she thinks they're her friends, so they become friendly. Bordering on Mind Screw, this works the other way as well: Dr. Clef frightened her, and she believed he wanted to kill her, so he became obsessed with killing her.
Clingy MacGuffin: Numerous SCPs fall under various categories of this, both mental and physical. To name but one example, SCP-1545 is a two-man llama costume that forces whoever dons it to become "Larry the Loving Llama", an identity they will maintain until they either die or are removed from the costume by others. And this is one of the more benign examples, as "Larry the Loving Llama" won't resist being taken apart even though he isn't inclined to do so of his own accord.
Clock Punk: SCP-217 is a virus that gradually and painfully turns any animal's organs (including humans) into gear-and-cog-driven machines.
Cloning Blues / Expendable Clone: SCP-1610 is a mysterious liquid that can make six clones out of one person without harming the original. The clones are okay with their situation (they're not supposed to be sapient), it's their creators who had problems with them, especially after turning their head researcher and his loyal secretary into test subjects:
Prometheus Labs researcher: I didn't come to work here so that I could commit murder over and over again. We're making no fucking progress and the higher ups fucking know it. The project should've stopped after the first week. Goodbye. I'm burning my body so you bastards can't fucking kill me more than I want to be killed.
Another researcher: I only wanted to help. All we've done is make humans that want to be killed. It crossed the line when they programmed in the phrase, "I wanted to die."
Combo Platter Powers: Allowing for humanoid SCPs has resulted in many a Mary Sue being listed. These are generally deleted within time, but the notoriously bad ones are decommissioned: they remain in the series continuity as past SCPs and are given elaborate destruction sequences.
Comedic Sociopathy: Invoked by the special containment procedures for SCP-3467-J, who is to be made fun of at every moment, even if he's trapped with SCP-682.
The SCP reports are written in an entirely serious tone, no matter how absurd the topic might be - a cake platter that continually generates cakes of various sizes sounds silly, but it's there and has to dealt with, as left unchecked it would bury the entire world under baked goods. Thus, the dry manner of the archive acts a Straight Man to the nature of the SCPs (especially the "joke" ones) and the eccentric behavior of SCP personnel.
The dead serious warnings after some doctors with a sense of humor pull some sort of stunt/prank.
The Computer Is a Cheating Bastard: Literally with SCP-1633, an unfinished video game that, if played long enough (and with enough breaks), starts actively targeting the player, not their in-game avatar. It's also been observed to exploit glitches in the physics engine, even ones unknown to the player prior. An attempt to bypass this by playing one continuous game resulting in the game rendering the guy catatonic in apparent retaliation once he started a New Game+.
Cosmic Horror Story: Perhaps at an even greater level than Lovecraft's, as the Foundation hasn't even been able to catalog the number of parallel universes, pocket dimensions, and indescribably vast voids full of incomprehensible entities and forces trying to kill us.
Cosmic Retcon: SCP-140 is a book describing the history of the horrifically evil and extremely advanced Daevite civilization. At the end of the book, they're wiped out. However, any time it gets anywhere near ink, shed human blood, or other fluids suitable for writing, it grows, extending the period of the Daevites and creating new traces of their civilization. When first recovered, the Daevites were squished by Qin Kai in the 3rd century BCE. Now? They were squished by Genghis Khan. The reason it's classified Keter is because enough ink could bring the Daevites into the present day, and it's a fair bet current human civilization wouldn't be a match for them. Oh, and just in case you feel safe, they don't have every copy.
Crap Saccharine World: Several SCP's are towns, locations, or areas where things are too good to be true for any that inhabit it.
Crossover: These are generally frowned upon; there used to be a lot of joke SCPs which were nothing more than "It's that thing from that show, and here's how the SCP foundation would describe it!", and they got eventually deleted. However, Clef's "Project Crossover" is a challenge to write a good crossover story—or, a good bad crossover story.
Cult: Many are known enemies of The Foundation and many worship/created different objects.
Church of the Broken God: Three branches, one Clockpunk,one Steampunk, one Cyberpunk all of which practice Machine Worship. As the name implies, they worship a broken mechanical god. Split into three branches, one of which claims that SCP-882 is the "heart" of their god. They also show interest in SCP-217 and SCP-271. The implications of a union between these objects is disturbing.
The Serpent's Hand: This group considers The Foundation to be unenlightened, they embrace the use of Paranormal objects and hold humanoid SCP in high esteem. The note in this security breach references "Black Surtr" as well.
The group responsible for the creation/impregnation of SCP-231, "The Children Of The Scarlet King".
[It is determined that this is the point where Dr. Clef accidentally fell out of his chair and struck his head nine times against the corner of the desk, fracturing his skull and snapping his neck between the second and third vertebrae.]
Darker and Edgier: The Never Hungry Man was changed from an SCP who was released back into the general public when his condition posed no threat to a man with worms that have faces in his stomach that leap out at people. In fact, this is typically the fate of many SCP drafts whom are said to be either too bland or not have a good hook. Then again, sometimes there's too much senseless edginess, and some needs to be Dummied Out.
SCP-299 is "an arboriform organism" that makes plants hard, black, pointy, and covered in prehensile vines; it also releases chemicals that make humans paranoid and aggressive.
Parodied with SCP-1049-J, a black fluid that turns objects into "darker" versions of themselves. ("Darker" in this case means "made of rusty metal with lots of spikes and skulls sticking out".)
Dark Is Not Evil: SCP-1471 (appearing to anyone using an app by the name of "MalO" for a sufficient amount of time), a large humanoid mass of shaggy black hair with a canine skull for a face, makes no attempt to actively harm anyone. Mostly it just wants to hang out. The problem comes from the fact that it won't leave you alone.
Deadly Euphemism: "Terminated" is used very frequently. The page on the Ethics Commitee lampshades this.
Cassy could be seen as one of the concept of Medium Awareness, as rather than take advantage of it, she slips into an existential crisis upon realizing that she's not technically real.
Delivery Stork: Horrifically inverted by SCP-918, a group of storks that spirit away newborn children to be harvested and turned into cosmetic products.
Depending on the Writer: Regarding the SCP Foundation itself. Although there is a general set of guidelines that everyone should follow for writing articles, the specifics are less well defined and each author has to decide for themselves how to handle them.
Determinator: SCP-682, the Hard-To-Destroy-Reptile is the embodiment of this. Regenerating after all attempts to destroy it (the SCP Foundation claims not to possess any means of doing so effectively), while generally shrugging off any damage to the point it has been described as being "seen moving and speaking with its body 87% destroyed or rotted"
Deus ex Machina: SCP-2000 is a Thaumiel-class object that can effectively recreate humanity after an end-of-the-world event. The name of the object is "Deus Ex Machina". Horrifyingly enough, it's actually been used several times already.
Did You Just Flip Off Cthulhu?: Eldritch Application, where the Foundation director refuses to take Zalgo in as SCP since it's too vaguely defined, all-encompassing and hasn't ever done anything worth containing, which causes it to admit defeat and leave in shame. The ending hints that Cthulhu will get similar treatment as well.
Did You Just Punch Out Cthulhu?: Any time a Keter class gets detained effectively (which is very, very rare) or even detained at all, it's this. Special mention goes to the Agent who managed to murder Able several times (gaining Able's respect) before an airstrike killed him, and an Agent who managed to contain SCP-058 after its rampage by squashing it under a tank. Decommissions are often this, except when done by Clef.
Doing in the Wizard : Averted. For a site that prides itself on clinical detachment and scientific inquiry, it is almost impossible to discover how nearly all of the SCPs actually work, where they came from, or why anyone would want to make some of them. They give it a good try, but it's not as important as knowing how to keep them safe and under control. If they ever came across a real wizard, they'd measure his staff, subject him to "stress" tests to determine destructibility, and finally have some very strong words with him over the creation of Eldritch Abominations. And, of course, they'd want to see if his magic could kill SCP-682.
Writers are pretty much encouraged to make sure that whatever SCP entity they write either hard to comprehend or flat out incomprehensible.
In-universe, if something becomes understood in enough detail then it's no longer considered paranormal, it gets "-EX" appended to its name, and the research done on it is released to the public.
Dream World: SCP-1230, a book where the subject can live out their fantasies. Their guide, the Bookkeeper, is friendly and the dreamworld can't harm them. Unfortunately when the subject works at the Nightmare Fuel Factory known as the SCP, well, see the next item.
Driven to Suicide: Commonly happens among Researchers, Agents, and D-Class personnel.
SCP-978 is a camera that shows whatever the photographed person most wants to be doing. In the Extended Test Logs, when Dr. Bright was photographed with it, it showed a tombstone saying "Jack Bright, resting at last."
A research team hypothesized that rollerblades are, technically, vehicles. We tested their hypothesis by having Gerald skate into the ORIA's headquarters in Tehran. They were right.note The building went up in a giant explosion.
Drinking Contest: SCP-1212 is a bar stool that mentally transports the sitter into various drinking establishments and forces them to enter a drinking contest that only ends after one hour has passed or the sitter dies (if they go unconscious SCP-1212 forces them to keep drinking).
Entity/entities in SCP-1212's "bars": "You must drink with me, in memory of those who sat where you sit and lacked the strength to understand their limits," and "We must curse those who were weak, and honor those who were strong."