The Fear Mythos is a spin-off of the Slender Man Mythos that evolved into an independent entity. Created in February 2011 by CuteWithoutThe, alliterator, and Lizard Bite, the mythos quickly gained a cast of writers who came up with hundreds of blogs and a colourful collection of Fears.
Over the years, the Fear Mythos eventually settled on a no-unifying-canon policy, allowing all writers complete freedom. In May 2012, this became official with the setting-up of the series bible, now obsolete. In April 2013, The Slender Man and The Rake ceased being advertised on the bible as official Fears, making the Fear Mythos officially independent (though affirming that writers could still use these creatures as Fears in their stories as much as they wanted).
In January 2015, a manifesto was created to replace the series bible that serves to sum up what the mythos has become. The manifesto is available in blog and vlog format.
The Fear Mythos currently has a decent-sized community spread out among a forum, this Wiki, and a Facebook group. Its stories are primarily literature, though visual narratives have been created too. Most stories set in the Fear Mythos are horror, however there have been many of other genres utilized.
To create a story within the Fear Mythos, all that is required is the story either contain a character, creature, or a motif that the author acknowledges is a Fear, or simply having the story take place in the same universe as another story that was set in the mythos.
The Fear Mythos consists of as many fictional universes and canons as is necessary to include every story created for it. Every author is entitled to his or her own canons and is not required to write in anyone else's unless he or she specifically wants to. The Fears are open source; no story will be labelled as "fanfiction" unless the author specifically says so (with exceptions made for stories featuring other authors' non-Fear characters such as Joseph Steward or Tav Lowe which are not open source).
Stories also do not have to be horror, and Fears do not have to be portrayed in any specific way.