Adam B. Vary's long piece at Buzzfeed about the making of Clue is wonderful. Did you know that they almost hired the playwright Tom Stoppard to write the script? ("Stoppard toiled on a script for Clue for a full year — and then he hit a wall too. “I’ll never forget it,” says Landis. “I got a letter from him, literally a year later, on this beautiful onion-skin paper, very elegant stationery, basically saying, ‘I give up!’ And he enclosed a check for the entire amount he was paid.") Stephen Sondheim and Anthony Bates from Psycho were the backup picks to write the screenplay, which director Jonathan Lynn ended up doing himself. Lynn also tried to get Rowan Atkinson for Wadsworth, and Carrie Fisher for Miss Scarlett (the latter fell through due to a rehab situation: "She sniffed a lot, and she said she had hay fever, which of course I believed... I didn’t know that everyone in Hollywood was snorting cocaine," the director said). The eventual cast became close quickly, because of all their group scenes. "It was like trying to herd a bunch of puppies," said Lesley Ann Warren, who replaced Carrie Fisher as the vamp.
Vary also includes a tribute to the best part of the movie, which is also the only improvised part:
[F]or many Clue faithful, this is The Moment, when the movie passes through the threshold from genuine enjoyment to something approaching love — think Roy Scheider saying, “You’re gonna need a bigger boat” in Jaws. It comes toward the very end of the film, when Mrs. White is confronted with her hatred of Yvette for sleeping with her husband. “All that was written was, ‘I hated her so much that I wanted to kill her,’ or something like that,” says McKean, still smiling from the memory. “But she just kind of went into a fugue about hatred. She did it three or four times, and each time was funnier than the last. I thought that they could have strung a bunch of them together because they had plenty of cutaways of all of us going, What the fuck is she talking about?”