Songfacts®:

• In 2010 Slash founded Slasher Films, a horror film production company. The former Guns N' Roses guitarist co-wrote the soundtrack for its first motion picture, Nothing Left to Fear, which was premiered on October 4, 2013. This song was influenced by Slash's time in the film world. He told Artist Direct: "When I write music for movies, a different side of me as a musician comes out. I really liked that side. It's something I never apply to the confines of a rock band who's doing songs at roughly around four minutes long. It's not as a rule, but it just never happened."
  
  "I thought, 'God, I'd just love to sit down and write thematically in the context of the band as opposed to only doing it for cinema and visuals,'" Slash added. "'The Unholy' was the result of that, and it still ended up being seven minutes long. It started out like it does on acoustic."
• Slash told Premier Guitar magazine that he used his Goldtop '57 reissue guitar on World On Fire, "for that creamy stuff where it's sustainy smooth where I turn the tone down." That included the guitar solo at the very end of this song.