Okay, class. It has come to my attention that some articles have been using the term "meme complex" incorrectly. I've always been fascinated by memes and meme complexes, so this gives me a chance to explain everything.
What Is A Meme?
So the first thing we have to explain is: what exactly is a meme? You may have heard about memes, actually -- they are everywhere on the internet. If you've ever heard the phrase "all your base are belong to us" or "I can haz cheeseburger?" or "suprise, bitch," you have encountered an internet meme.
This is not the type of memes I am talking about.
Richard Dawkins was the first to name memes in his book The Selfish Gene: "We need a name for the new replicator, a noun that conveys the idea of a unit of cultural transmission, or a unit of imitation. 'Mimeme' comes from a suitable Greek root, but I want a monosyllable that sounds a bit like 'gene'. I hope my classicist friends will forgive me if I abbreviate mimeme to meme."
"Examples of memes are tunes, ideas, catch-phrases, clothes fashions, ways of making pots or of building arches. Just as genes propagate themselves in the gene pool by leaping from body to body via sperms or eggs, so memes propagate themselves in the meme pool by leaping from brain to brain via a process which, in the broad sense, can be called imitation."
You can see where this definition of meme became the current, internet meme: the use of imitation, the repeating of ideas (see: lolcat, doge, seventy percent of Tumblr).
"When you plant a fertile meme in my mind you literally parasitize by brain, turning it into a vehicle for the meme's propagation in just the way that a virus may parasitize the genetic mechanism of a host cell."
The study of memes is called memetics.
What Is A Meme Complex?
A meme complex or memeplex is a group of memes. Just as certain genes can group together to create gene complexes, so can memes.
Richard Dawkins uses the example of organized religion: "Perhaps we could regard an organized church, with its architecture, rituals, laws, music, art, and written tradition, as a co-adapted stable set of mutually-assisting memes."
Another example of a meme complex would be Christmas. Think about all the rituals associated with Christmas: Christmas trees, carols, candy canes, Santa Claus, elves, et cetera. All of these are memes which connect to one another creating a meme complex.
So What Does This Have To Do With The Fear Mythos?
Ah, my dear Watson, you have come to the crux of my argument: all of the monsters in our menagerie are memes.
The Slender Man is a meme. Think about it: when it first appeared, the idea of it struck a chord with people, who replicated and imitated it. And not just that, other details about the Slender Man began to attach themselves to the meme: facelessness, forests, cryptic symbols, distortion. All of these things became memes and attached themselves to the Slender Man creating a meme complex.
This is not In-Game, by the way, this is Out-of-Game. The Slender Man is, in all seriousness, a meme complex. (One could argue that the Fears are only memes, not meme complexes themselves, but the Fear Mythos overall can be seen as a meme complex as well.)
I like to refer to the Slender Man and the Fears as memetic monsters.
What About The Panopticon?
The Panopticon is an In-Game group that seeks to eradicate the Slender Man and the Fears. They used to be a government think tank looking into the phenomena of "runners" and "proxies" until they actually caught a glimpse of the Slender Man. They convinced themselves that Slendy was a meme complex so powerful that just having it in your head caused you to hallucinate him. All evidence against that concept was swept away and rationalized as something else.
They sought to eliminate the "Slender Man meme complex" by brainwashing those who believed in it. Make them disbelieve in the meme, remove the meme complex from their head. To this end, they used another meme and tried to instill it into people's minds: "This is the best of all possible worlds."
Now, whether the Panopticon is right or wrong is up to you. If they are right and all the Fears are meme-complexes, brainwashing runners and servants might be the only way to defeat them (although the memes could spread faster than they are eradicated). In Don't Let Them Tell Us Stories, the Panopticon is decidedly wrong and their methods are purely harmful.
So there we go.