Robert W Chambers invented this fictitious play, which has
the effect of driving its readers picturesquely insane. He
only gives a few lines of it in his stories that mention it,
which you may read here: http://www.yankeeclassic.com/miskatonic/englishl/chambers/kinginye/contents.htm but that hasn't kept three or four people from trying to imagine
the rest:

Thomas Ryng (available from Armitage House):
http://www.tccorp.com/armitage/ah_productlist.html

James Blish (in the short story, "More Light")

Valerian Caprice (Act I only)

& an appropriately anonymous version 

TheKingInYellowByGraywyvern. ''Anonymous? The identity of Graywyvern can be discovered by googling him and looking at the eleventh hit, which is on result page two.'' (Sherlock will be proud...)

See: http://myweb.worldnet.net/~c_thill/chambers/presgb.html (BrokenLink in 2002, archived at http://web.archive.org/web/20011029173603/http://myweb.worldnet.net/~c_thill/chambers/presgb.html) for a very comprehensive overview.

For an idea of what it has spawned, see: http://www.yellowsign.homestead.com/ (BrokenLink in 2002)

For a movie based on Chambers's book see: http://www.carollus.demon.co.uk/repairer/outline.htm (BrokenLink, archived at http://web.archive.org/web/20010908140953/http://www.carollus.demon.co.uk/repairer/outline.htm, but see also http://www.repairerofreputations.com/ and http://www.unfilmable.com/newsDecember04.html)