Question: What year was H.P. Lovecraft's novella "At the Mountains of Madness" published and was the first appearance of The Elder Things?

Context paragraphs:
The Willows (story): "The Willows" is a novella by English author Algernon Blackwood, originally published as part of his 1907 collection "The Listener and Other Stories".  It is one of Blackwood's best known works and has been influential on a number of later writers.  Horror author H.P. Lovecraft considered it to be the finest supernatural tale in English literature.  "The Willows" is an example of early modern horror and is connected within the literary tradition of weird fiction.

Mountains of Madness (EP): Mountains of Madness is American thrash metal band Diamond Plate's EP, self released in 2008.  Also re-released on Stormspell Records as a split CD with Oppression.  Some people believe the EP was recorded at Beyond the Gates recording studio, but it was actually recorded in Konrad Kupiec’s basement.  The song "At the Mountains of Madness" relates directly to the H.P. Lovecraft story by the same name.

Henry Everett McNeil: Henry Everett McNeil (1862 - December 1929) was a leading children's author of the 1910s and 1920s, and was an original and core member of the Kalem Club circle around the writer H. P. Lovecraft.  McNeil played a crucial role in the career of H.P. Lovecraft, in that he was the first to urge Lovecraft to submit his fiction to "Weird Tales" magazine in the early 1920s.

The Mountains of Madness: "The Mountains of Madness" is an audio/visual musical adaptation of the works of H.P. Lovecraft by Tiger Lillies, Danielle de Picciotto & Alexander Hacke.  It was conceived by Hacke in 2005.  Tiger Lillies performs the music while Hacke narrates selected pieces of Lovecraft's work.

At the Mountains of Madness: At the Mountains of Madness is a novella by American author H. P. Lovecraft, written in February/March 1931 and rejected that year by "Weird Tales" editor Farnsworth Wright on the grounds of its length.  It was originally serialized in the February, March, and April 1936 issues of "Astounding Stories".  It has been reproduced in numerous collections.

The Taking of Planet 5: The Taking of Planet 5 is a BBC Books original novel written by Simon Bucher-Jones & Mark Clapham and based on the long-running British science fiction television series "Doctor Who".  It features the Eighth Doctor, Fitz and Compassion.  It is, in part, a sequel to the television serial "Image of the Fendahl".  It also features references to many elements from the Cthulhu Mythos stories of H. P. Lovecraft, in particular the Elder Things and their ancient Antarctic city from "At the Mountains of Madness".

Elder Thing: The Elder Things (also known as the Old Ones and Elder Ones) are fictional extraterrestrials in the Cthulhu Mythos.  The beings first appeared in H. P. Lovecraft's novella, "At the Mountains of Madness" (published in 1936, but written in 1931), and later appeared, although not named, in the short story "The Dreams in the Witch-House" (1933).  Additional references to the Elder Things appear in Lovecraft's short story "The Shadow Out of Time" (1936).

Lovecraft Country (novel): Lovecraft Country is a 2016 dark fantasy horror novel by Matt Ruff, exploring the conjunction between the horror fiction of H.P. Lovecraft and racism in the United States during the era of Jim Crow laws, as experienced by black science fiction fan Atticus Turner and his family.  It was published by Harper Collins.

Yig: Yig (the Father of Serpents) is a deity in H.P. Lovecraft's Cthulhu mythos.  He first appeared in the story "The Curse of Yig", which was created by Zealia Bishop and almost completely rewritten by Lovecraft.  In this story he is described as "shapen like a man, except ye look at him clost."  According to Lovecraft, one of Yig's main characteristics is his devotion to snakes - his "children" - he punishes those that harm them by turning them into spotted snakes.

Elder Sign (card game): Elder Sign is a cooperative card and dice game, based on the Cthulhu Mythos of horror writer H.P. Lovecraft and Chaosium's Call of Cthulhu roleplaying game.  It is published by Fantasy Flight Games, which also produces the Cthulhu Mythos games "Arkham Horror", "", "Mansions of Madness", and "Eldritch Horror".

Supporting paragraphs: Elder Thing At the Mountains of Madness
Answer: 1936