Giacchino said the special was inspired by horror films from the 1930s and 1940s, comparing it to the film Poltergeist (1982), which was a major influence for the special, in that it would have "the right level of scares". Other inspirations included The Twilight Zone, King Kong (1933), and The Wolf Man (1941), with Giacchino calling Werewolf by Night a "love letter" to these horror inspirations. Additionally, Giacchino tried to approach the special with a "moral center" beyond "just blood and guts". Disney+ stated that the special would "evoke a sense of dread and the macabre, with plenty of suspense and scares along the way". Feige called the special "fun", adding that it was also "a little darker [and] a little scarier" than the studio's other content. Elements of the Werewolf by Night character were altered from the comics to allow the story to work in a more modern setting; Quinn had been inspired by the Werewolf by Night issues "Carnival of Fear" and "The Danger Game". The special also features Man-Thing, at the suggestion of Feige. Man-Thing is only referred to as Ted in Werewolf by Night, with Giacchino wanting to call him by his actual name as "a way to humanize him". There were also considerations to refer to him as a "Giant-Size Man-Thing" (a reference to one of his comic book titles) but this and others "never felt quite right" and seemed "a little too cheeky".
