The Advent of Uhvash is a short story by James Ambuehl.
A man is invited to visit his friend bringing with him some books on "Black Magic". It transpires that his friend has begun to experiment with intense Astral Projection, assisted by one Great Old One, Gi-Hoveg, in defiance of another Great Old One, Uhvash. It ends very badly for the narrator's astrally projecting friend.
Behind the Mythos
Treading very well worn ground, the story features a laundry list of namechecked books related to the Mythos although the ones referred to are almost all of the author's own invention rather than from the work of previous decades by Lovecraft himself or the Lovecraft Circle. The texts named are "the accursed Blood-Rituals of Rhylkos", Cultes des Goules,THE R’LYEH TEXT: FRAGMENTARY TRANSCRIPTIONS, the Confessions of the Mad Monk Clithanus, the Caelano Fragments, the Clavicule Cosmopgraphicum, The Ultimate War, Devil-Gods of the Lu-Kthu Mythos by Linwood Carter, and finally the Book of Non Amya. Doctor Strange from Marvel Comics is also namechecked, indicating that the Ambuehl contributions to the Mythos all take place in a universe where Marvel's own appropriations from the Mythos are definitely fictional.