Trivia / Billy & Mandy's Big Boogey Adventure

• Celebrity Voice Actor: George Segal as Horror.
• Keep Circulating the Tapes: Much like Season 1 of The Grim Adventures of Billy & Mandy, the film was released on DVD, but has long since gone out of print, which makes the prices of copies found online pretty high. Other than that, you had to rely on recordings from the Cartoon Network broadcast and hope it wouldn't be taken down due to copyright. But as of June 2021, it is now available for streaming on HBO Max in Latin America.
• Production Foreshadowing: It may have been unintentional, see What Could Have Been below, but Numbuh 3 making a cameo in this movie would soon be followed up with a crossover between the two shows later that same year.
• Throw It In!: While recording the end of the Scary-o Song, Richard Steven Horvitz improvised Billy's last singing line "I could use something to eat, I'm really really hungry!" It was mostly due to the fact that the production crew had recorded the song so many times that they started to feel hungry themselves.
• What Could Have Been:
  • According to Maxwell Atoms, Seth MacFarlane was initially supposed to share the role of the 2 Headed Parrot with his sister, Rachael MacFarlane. But Seth's film Ted got the greenlight, which led to his unavailability. As a result, Rachel voiced both of the heads.
  • Also according to Atoms, Grim was supposed to be replaced by an entirely new Grim Reaper character, with the hopes of casting a known celebrity. Atoms initially had Pamela Anderson in mind for the role, but the executives rejected it, wanting a more big-named celebrity. After making a list of potential candidates (Marilyn Manson, Drew Barrymore, Elijah Wood, etc.), the executives brought their one list of celebrities that were either practically unavailable or had high rates (one of the candidates was Angelina Jolie). Due to lack of time, Atoms settled on Numbuh 3 instead.

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