Basic Trope: Rather than end how you think it will, the story takes a sharp turn and ends a different way.
Straight: Colonel Mustard wasn't murdered, he committed suicide and framed his wife!
Exaggerated: He wasn't murdered by any one of the suspects... because Everybody Did It! Then it turns out that he wanted to be murdered anyway to help the detective and his assistant who were disguised to supposedly investigate his murder. And then his brother was murdered by a random junkie on the street instead of any of the previous characters involved, who then committed suicide. A Tyrannosaurus rex comes and eats everybody, including himself.
Downplayed: The evidence against Mrs. Mustard is shaky, but the alternative — that Col. Mustard committed suicide to frame her — is far fetched. The detectives decide the best they can do is hope the D.A. and a jury can sort it out.
Justified: That his wife made his life so miserable, his daughter got cancer and he was unable to pay for treatment due to going bankrupt pushed him over the edge. This whole scheme was for the daughter to get his insurance money. It was inevitable.
Double Subverted: The butler was framed by his wife.
Parodied: Who was in turn manipulated by her late husband, who had committed suicide long before he was "killed".
Zig Zagged: It seems it really wasn't Mrs. Mustard, only it turns out it was! However, that was all a manipulation by an unknown third party, however they were contracted by her as a plot to seem innocent by default, so it really was her.
Lampshaded: "It's a murder mystery, there's always a twist somewhere in the case."
Invoked: Mrs. Mustard pleads with the detectives that she's smart enough to know her estranged relationship with her late husband makes her the top suspect, and that she's smart enough that all the clumsy evidence pointing to her is simply too convenient. It's "obviously" a set up.
Exploited: Before his suicide and frame up of his wife, Col. Mustard realizes that there's a good chance the detectives will discover the ruse. So instead he switches his scheme backwards to make his suicide look like a cover up for a murder done by his wife. Essentially he's using a subverted Untwist and counting on the detectives thinking there's only one Twist in the story.
Discussed: "This isn't like in the movies, a giant pterodactyl isn't going to swoop down and change everything in the end of the third act.
Conversed: "This show always has a Twist Ending. By now you'd think the characters might make some contingency plans for inevitable pterodactyl attacks."
Implied: The detectives arrest Mrs. Mustard after a standard investigation reveals she's the one who murdered Col. Mustard. However the detectives close the case with a bad feeling they can never put their finger on, and viewers who rewatch the episode can deduce she was framed from background evidence.
Deconstructed: Just when the mystery seems wrapped up, a shocking revelation turns everything on its head. However, rather than accept this turn of events the detectives realize it's a little too convenient and see it as a last, desperate gambit by one of the suspects and react accordingly.
Reconstructed: Only to realize that this strange twist of the case was unavoidable and would have happened whatever they had done.
Plotted A Good Waste: It looks like it's going to be another case of the murdered in reality being the criminal. But it isn't, he really was an innocent(ish) victim.
Played For Laughs: The Mouse falls on the real culprit, panicking them into dropping key incriminating evidence.