On publication, it was widely denounced by the press as degenerate and horrific because of its implied sexual content, and the novella hurt Machen's reputation as an author.

Shortly after an explanation to her mother that is unrevealed to the reader but instills great revulsion in Clarke, Rachel returns to the woods and disappears forever.

Helen has a very abnormal death, transforming between human and beast, male and female, and dividing and reuniting, before turning into a jelly-like substance and finally dying.

Machen's lifelong fascination with occultism began after he read an article on alchemy in an edition of Charles Dickens's periodical Household Words belonging to his father, a clergyman.

[1] Machen felt that he had "transliterated [the feeling] clumsily" in The Great God Pan, elaborating: "I translated awe, at worst awfulness, into evil; again, I say, one dreams with fire and works in clay.

Once he decided the two stories were connected, Machen wrote the rest of The Great God Pan in a single evening save for its final chapter.

[7] When published as a book, The Great God Pan was accompanied by another Machen tale called "The Inmost Light"[8] which also features a mad scientist and elements of science fiction.

[11] The novella has been classified as Decadent literature as well,[8] as it features hallmarks of the genre such as "occultism, paganism, non-mainstream eroticism, sexual diversity, the femme fatale, violent and strange deaths, and the simultaneous investment in and disavowal of bourgeois identities.

[14] The phrase, "the great God Pan" comes from an ancient Greek folktale recorded in Plutarch's De defectu oraculorum (On the Decline of Oracles),[14] which claims that a Greek sailor near the island of Paxi during the reign of Emperor Tiberius (ruled 14–37 AD) heard a voice cry out, "When you are arrived at Palodes, take care to make it known that the great God Pan is dead.

"[14] As a member of the Decadent movement, Machen sought to subvert traditional themes and transgress literary boundaries,[14] an agenda which made Pan a particularly appealing figure.

[2] The works of Robert Louis Stevenson, especially his 1886 novella Strange Case of Dr Jekyll and Mr Hyde, were among Machen's most significant influences when writing The Great God Pan.

[21] John C. Tibbetts observes similarities between Helen Vaughan and Ayesha, the sexually liberated demonic priestess from H. Rider Haggard's She: A History of Adventure (1886).

"[23] The novella is characteristic of a late nineteenth-century interest in paganism in general and Pan in particular that is found in the works of Florence Farr and Kenneth Grahame.

[25] According to the British scholar of modern literature Roger Luckhurst, Raymond expresses a typical Neoplatonist view of reality in which the true object of study is the revelation of a "higher, hidden spiritual world".

"[18] Neoplatonism is also commonly regarded as the last school of pagan philosophy[18] and Raymond's views therefore relate back to the recurring theme of the death of Pan.

[18] Author Theodora Goss sees The Great God Pan as equating paganism with irrationality and what Carl Jung would call the collective unconscious.

[27] Black Gates's Matthew David Surridge believes that the story associates paganism with sex and femininity, while portraying Helen as a female Antichrist,[2] a view shared by James Goho in Journeys into Darkness: Critical Essays on Gothic Horror (2014).

[28] The Great God Pan's implied sexuality caused a scandal upon its original release and hurt Machen's reputation as an author.

[2] Reviewing the novella for the magazine Literary News, Richard Henry Stoddard criticised the story as "too morbid to be the production of a healthy mind".

[30] Quilter declared: "'The Great God Pan' is, I have no hesitation in saying, a perfectly abominable story, in which the author has spared no endeavour to suggest loathsomeness and horror which he describes as beyond the reach of words.

"[31][32] Quilter warned that Machen's books were a dangerous threat to the entire British public and that they would destroy readers' sanities and senses of morality.

[33][31] Quilter went on to attack the story's publisher, John Lane, as well as Machen himself: "Why should he be allowed, for the sake of a few miserable pounds, to cast into our midst these monstrous creations of his diseased brain?

[38] Dennis Denisoff connects Machen's tendency to make his empowered female characters "sexually monstrous" to his criticisms of authors who discussed the subject of women's rights.

[44] Black Gate's Matthew David Surridge said that The Great God Pan influenced Bram Stoker's Dracula (1897) as both works feature "an introductory sequence featuring a horrified Englishman in a non-English setting; then a variety of seemingly-unconnected events in London, the metropole at the heart of Empire; then the discovery that all those events are in fact inspired by one malign and supernatural intelligence, that the rational contemporary capital is threatened by the irrational and archaic; then an equivocal conclusion.

"[2] John C. Tibbetts notes that both Helen Vaughan in The Great God Pan and Lucy Westenra in Dracula are "demon women of voracious and malignant sexuality".

[26] Tibbetts also notes that Machen's portrayal of Helen Vaughan as demonic and hyper-sexual may have influenced a similar character, The Woman of Songs, in Richard Marsh's The Beetle (1897).

[46] Pan's depiction of a monstrous half-human hybrid inspired the plot of Lovecraft's "The Dunwich Horror" (1929), which refers to Machen's novella by name.

[47] Clark Ashton Smith was inspired by The Great God Pan to write his story "The Nameless Offspring" (1931), which also features a monstrous child born of a human and a supernatural entity.

[49][50] The Great God Pan influenced Peter Straub's novel Ghost Story (1979) in its depiction of a shapeshifting monster who terrifies those it encounters.

[52] Del Toro deliberately chose to imitate the darker, more sinister fauns of Machen and Blackwood rather than the "sweetly domesticated figure" of Mr. Tumnus from C. S. Lewis's The Lion, the Witch and the Wardrobe (1950).