- Acting for Two: Robert Musselman, who plays Ballerinaman reappears later in the film as a Disco Boy.
- All-Star Cast: Ben Stiller, William H. Macy, Greg Kinnear, Geoffrey Rush, Paul Reubens, Hank Azaria, Janeane Garofalo, Kel Mitchell, Eddie Izzard, Tom Waits... maybe this is why the title of the song Smash Mouth made accompanying the film is "All Star."
- Awesome, Dear Boy: Janeane Garofalo had originally turned down the the part of The Bowler, but changed her mind when she heard William H. Macy and Geoffrey Rush had signed on.
- Box Office Bomb: A domestic take of $29 million with a small addition of $3 million internationally came nowhere close to recouping the film's $68 million budget. Being released on the same day as The Sixth Sense didn't help.
- Breakaway Pop Hit: "All Star" by Smash Mouth was one of the most popular songs of 1999 and appeared on the Mystery Men film and soundtrack months before the release of their album Astro Lounge. Its high-concept video features all the main cast members of Mystery Men...who were then later cut out after the song far eclipsed the movie in popularity. "All Star"'s subsequent appearance in dozens of movies in the next few years only muddied the waters of its original origin. To rub salt on the wound, "All Star" has gained notoriety as an internet meme...but videos featuring the song tend to attribute it to Shrek, a (albeit, far more successful) film that premiered two years after "All-Star".
- Creator Killer: More like Stillborn Creator. The film's financial failure led to it being the only non-commercial job for director Kinka Usher, who made his cinematic debut with this film.
- Deleted Role: Luis Guzmán played the part of a Mexican restaurant owner but his scenes were deleted from the final print.
- Enforced Method Acting: Janeane Garofalo wasn't told that Captain Amazing's charred hand would break off when she touched it, which genuinely freaked her out.
- Fake American: Claire Forlani (Monica) and Eddie Izzard are British.
- Fake Nationality: The Blue Raja, but it's part of his schtick. Also, Casanova is meant to come from a country that doesn't exist. He has a bit of German and Russian in his accent.
- Hostility on the Set:
I'm going back to commercials when this is done. I've had enough. I'd much rather do my cool little one-minute shorts that I make than deal with all this nonsense.
- According to Hank Azaria, the cast argued constantly with each other over the comedic tone of the film.
- Ben Stiller revealed in an interview with David Letterman that he and Greg Kinnear got into a heated argument on the set. Afterwards, Stiller tried to be released from the film.
- Azaria revealed in a 2011 interview with The AV Club that during production Kinka Usher declared
- Irony as She Is Cast: Prior to the film, Janeane Garofalo had no bowling experience. Funnily enough, her parents met at a bowling alley.
- Name's the Same: Alton Brown, on an episode of Good Eats devoted to waffles, also portrayed a character called "The Waffler."
- Old Shame: Artie Lange, who has joked about the poor reception of films he's acted in, considers this to be the worst movie he has made. After seeing his brief scene in the beginning of the film, his mother and sister called him from the theater to ask if he would have any more scenes because they wanted to leave.
- Playing Against Type: Somewhat with Jenifer Lewis. She's still playing the loud, strong black woman she usually plays, but, unlike most of her movies, where she plays people much older than her (for example, in The Preachers Wife, she played Whitney Houston's Mom and a Grandmother in her late 30's), she plays someone closer to her age, as she plays the mother of three kids who are all under 12.
- Recycled Set: A number of the sets used in the film are the same sets used in Batman Forever which makes sense as Champion City kind of lampoons the over-the-top architecture of Gotham City as seen in Batman Forever and Batman & Robin.
- Casanova's mansion is Whipstaff Manor from Casper.
- Throw It In!:
- A workman on the set threw a disposable lighter into a trash can, not realizing it was a prop that would later be set on fire. The lighter exploded during a take in a sudden burst of flame behind Paul Reubens (The Spleen) who improvised the famous "Excuse me" line. This was deemed to be hilarious so they kept it in the movie.
- Tom Waits had trouble memorizing his lines during his big monologue so he wrote them on his hands, which explains his odd stance and gestures. Fortunately the director thought this was perfect for his character.
- Unintentional Period Piece: Aside from some time period specific jokes and references, as well as its overall aesthetic, this retrospective piece on the movie points out that Mystery Men came out at a time when superhero movies were still generally considered campy and something only for the fanboys and the genre was still shakily trying to figure itself out, with more missteps than actual hits, a very far cry from how superhero movies would later become massive pop culture juggernauts a decade later by striking the right balance between fun and serious.
- What Could Have Been:
Trivia / Mystery Men