Matthew Patrick (or "MatPat"), a YouTuber known for making a multitude of Five Nights at Freddy's analysis videos throughout the series' history for his series "Game Theory", makes a cameo as a waiter in the 2023 "Five Nights at Freddy's" film. The coffee shop that he works at is named Sparky's (a nod to Sparky the Dog, one of the series' earliest fan-made hoaxes). MatPat's character's name as seen on his name tag is Ness, which, according to series creator Scott Cawthon, is a reference to a 2016 Game Theory video where MatPat theorized that Sans from Undertale was Ness from EarthBound. MatPat's final line in his scene is "but that's just a theory", a portion of his catchphrase used in the majority of his videos.

A pinned comment left by Cawthon on a "Film Theory" video where MatPat goes into further detail on his cameo in the film claimed that the packed theater Cawthon watched the film in "ERUPTED in cheers" when MatPat appeared.