Trivia: Much of the guitar work done in this film was by guitar hero Steve Vai, who also worked on PCU and, perhaps more famously amongst guitarists, Crossroads. Pretty much all the guitar licks which are played throughout the film when Bill & Ted play air guitar are played by Steve, as well as "The Reaper Rap" - in the end credits.
Trivia: The chant to get rid of evil that Missy and the "New Age Dudes" say which sends Bill and Ted to Hell is "Ed and Chris will rule the world" said backwards. Ed Solomon and Chris Matheson are the writers of the film. Watch this scene with subtitles on and you will see.
Trivia: In the seance scene, when Missy opens the book with the cover "Riddance of Evil" the text reveals it's actually "Four Seasons" by Stephen King. (This is just before she finds the page with the chant). Trivia, not a mistake, because the text is only visible by pausing.