Lets compose "Incusion Criteria" 

Ok, we leave it too long. I propose following criteria to incuding entries on this list.
 The element must has signification impact in the work. Simply "having word Cthulhu as grafiti in one comic panel" doesn't noaable enough. Nor does "having Deep One as one of minor enemies in games". "A Necronomicon can be spot on main character's bookshelf" doesn't count either. As enemy in games, the thing must be at least a major boss. The necronomicon must has vital role (and it must be Lovecraft necronomicon, second-hand derived from Evil Dead doesn't count).
 If the names are different from mythos, citation need. Nope, similar name isn't enough. You may think it's obvious, but there is chance that the name actually derived from something else or the author simply want weird name. In fact, many of deities in Aztec mythology has name as weird as Cthulhu.
How about that?