At the beginning of the film, Griffin O'Neal's Skip character is blamed for an prank-turned-accident which leaves a ferryman disfigured. In a bizarre case of life imitating art, O'Neal was indicted on manslaughter charges the following year for a drug-induced boating mishap that resulted in the death of Francis Ford Coppola's son Gian-Carlo Coppola.
While the crew was lighting a scene, Deborah Goodrich began reading a Cosmo questionnaire to her costars, which elicited a huge conversation that caught the attention of director Fred Walton. A few days later, Walton handed Goodrich the magazine and a new set of questions, and asked the actresses to improvise a scene which wound up in the final cut of the movie.
Deborah Foreman came in early to audition for Muffy, but the director and producers didn't feel she was right for the part. They were close to signing several other actresses who backed out for various reasons. Foreman really wanted the part and petitioned for another audition - she blew everyone away the second time around and landed the role.
According to director Fred Walton, Paramount executives didn't dislike the infamous deleted third act, they just felt that the movie would end on a higher note without it. However, producer Frank Mancuso Jr. insisted on tacking on the jack-in-the-box ending, which was shot in L.A. months after production had wrapped.
Another horror movie utilized the same title around twenty-two years later with 2008's April Fool's Day (2008). This unrelated picture was not a remake but was also a slasher movie and unlike this 1986 film which underplayed the gore off-screen, the 2008 film was more in the tradition of the usual gory slasher pic that this film evoked and spoofed.
The filmmakers had difficulty casting the role of Harvey. The rest of the cast and crew had assembled in Vancouver, except for producer Frank Mancuso Jr., who stayed in L.A., desperately trying to find an actor to portray Harvey. Finally, he found Jay Baker and whisked him away to the shoot, which worked out well since the Harvey character was a bit of an outsider.
During a 30th anniversary reunion screening/panel, Deborah Goodrich (Nikki) revealed that she was sent a script for an unproduced sequel several years after the film's release, though she was sketchy on the details and couldn't recall the names of the two writers. The story found Chazz and Nikki, who had gotten married, buying a closed-down porno theater on 42nd Street in New York City that they planned to turn into a bed and breakfast - but when one of Chazz's college-aged relatives arrived for a visit, the games began again. Ironically, Goodrich and her second husband bought the Avon Theatre in Stamford, CT, where this anniversary screening was held.
A novelization written by Jeff Rovin was published by Pocket Books in 1986. Rovin embellished in a few instances (Muffy's maid was black, Rob cheated on Kit, etc.) but generally it's very faithful to both the movie and Danilo Bach's screenplay. The book was the first big tip-off for fans that the entire third act of the film had been removed; subsequently photos from the lengthy deleted sequence surfaced on back covers of various home video editions.
A hangman's rope noose was formed out of the letter "P" and a dagger out the letter "Y" in the film's original 'April Fool's Day" promo title logos. Moreover, a hangman's rope noose was formed out of pony-tails hair of the poster's central female figure (meant to be 'Deborah Foreman') who also held a dagger behind her back.
When they began shooting the dinner party scene, director Fred Walton commented in a 2016 interview with Daily Dead that "there was no collective energy whatsoever" and the scene was "flat." When they broke for lunch, Walton scolded the cast and when they returned to film the rest of the scene, everyone stepped up their game.
The interior of the well scene was shot in tank on an L.A. soundstage at the end of production. The water was dyed to look murky and crew members discarded their cigarettes right into the tank. Deborah Goodrich (Nikki) spent so much time submerged in the nasty water that she left the set with a ear infection.
Although only mentioned once by Kit later in the film, the characters are students of Vassar: a private liberal arts college in New York. Muffy's van on the St. John's island property has a Maine license plate (and Clara the housekeeper speaks with a heavy New England accent) so it is implied that Muffy's summer home is off the coast of Maine.
The film originally had a much longer and more twisted ending. In the original script, after Muffy reveals the whole weekend was setup, the guests leave except for Rob, Kit, Chaz, and Nikki who sneak back to the house to prank Muffy for revenge. However when they return, Skip cracks and attempts to kill Muffy in a rage of jealousy. Rob jumps in and saves Muffy, killing Skip in the process. This ending actually was filmed but didn't make final cut as the studio opted for a more upbeat conclusion. This ending is identical to how the book plays out.
The film had an additional alternate ending scripted at one point. In that ending Muffy is left to believe she is alone on the island. Skip bursts out of a closet and 'cuts' Muffy's throat. She screams only to have the rest of the characters, thought to be gone, enter the room laughing - they pranked her back.
The ending and the final scene in Muffy's room were filmed three or four months after principal filming ended which explains the different hairstyles for Deborah Foreman and Leah Pinsent whom appear in the scene.
There are several clues throughout the film which foreshadow the twist ending: 1. In the very first scene, Muffy can be seen propping open the window in the cellar through which Kit and Rob crawl in and discover the clues. This was deliberate and crucial to the climax she had planned. 2. Nan says she met Muffy in Drama Society. Her acting ability proved to be a vital asset in order to portray her fictitious twin sister, Buffy. 3. Deborah Foreman's nails are painted red throughout the entirety of the movie, a subtle clue that Muffy and Buffy are the same person. 4. Muffy/Buffy announces that the water main must be broken; however, later in the evening, when Nikki is packing her bags, she absentmindedly turns on the sink and gets sprayed in the face with water, a clear indication that the water is working fine.