Slenderbone, a pornographic book on this very mythos. You did not read that wrong there is a pornographic book on the Slender Man Mythos! You can actually download that masterpiece if you google it, or if you don't have three dollars to spare watch MrCreepyPasta read it here.
What's even better, it'snottheonlypornbook written about Slender Man. The very fact they exist is hilarious on its own, but the fact you can buy them is all the more hilarious.