The climax of Curse of the Golden Flower after a couple Reveal-bombs are dropped ends up being something like this, with several different plots (sometimes literally) crashing into each other, including some that seemingly come out of nowhere.
The first two Pirates of the Caribbean movies show signs of this. The third one simply explodes with it in the scene where The Black Pearl changes owners about five times in thirty seconds (where half the cast suddenly reveal they've been plotting against everyone else for the Pearl). But for all the scheming and plotting, everybody ends up on exactly the side you would expect, i.e. pirates (plus Will and Elizabeth, who had pretty much become pirates by that point) vs. Davy Jones and the East India Company.
The diamond heist in A Fish Called Wanda goes off without a hitch, but then the gang starts plotting against each other. Wanda and Otto come back to the safe to steal the diamonds for themselves, with Wanda planning to steal them from Otto once he opens the safe, only to find that Ken already moved them at George's direction. Ken hides the safe deposit box key in his fishtank, but Wanda spots him checking and steals it, hiding it in her locket. George is arrested for the robbery, leading Wanda to try to seduce George's defence counsel Archie, to gain information (and probably to make Otto jealous), but finds herself becoming infatuated with him. Otto tortures Ken to get the location of the diamonds, but doesn't have the key, now that Wanda has decided to betray everybody, and incriminates George during his trial, instead of providing the alibi she previously promised. Finally, Archie and Wanda fly to South America with the diamonds.
The Lady from Shanghai begins with a discussion of how there are no tough guys, only people with an edge and people without one. Everybody thinks they're playing everyone else. The lead curses himself throughout the movie for being such an Unwitting Pawn.
The Big Lebowski. A trophy wife runs off for a weekend. Her nihilist friends pretend they've kidnapped her to squeeze money out of her rich husband to pay off a porn kingpin, whose goons had accidentally broken into the apartment of someone with the same name (the Dude) a few days earlier. The husband now calls up the Dude and asks him to deliver the "ransom" (actually an empty briefcase, while he pockets the money), expecting Dude to screw up to cover his tracks. Various other characters wander into the pileup, including a teenage car thief and Lebowski's angry ultra-feminist daughter (whose actually owns the business from which Lebowski embezzled the "ransom" funds), and Hilarity Ensues.
Snatch. Made particularly amusing by the fact that the only two characters who had absolutely no idea about the existence of the diamond that prompted so many characters to try and come up with so many plans are the ones who end up with it at the end.
The Court Jester was noted by many critics then and now as having an incredibly complicated plot for a '50s comedy, with a bunch of people who all have their own agendas getting in the way of or accidentally assisting each other. During the bulk of the film, there are three to four Batman Gambits going on at any given moment. The rebels want the key to the secret passage that will let them attack the castle, the princess wants to marry for love, several nobles want more power by having other nobles assassinated, and there's a witch with hypnotic powers who just wants to stay alive. Unfortunately, due to said hypnotic powers, the protagonist is unaware of all but one of these for most of the film.
What's Up, Doc?. Smith is chasing Jones, the hotel detective and the rich lady and the mobsters are chasing the jewels, Barbra Streisand (Judy) is chasing Ryan O'Neal (Howard), Howard and Hugh are competing for Austin Pendleton's fellowship, and it all culminates in a Chase Scene throughout San Francisco. Seriously, watch it.
Primer. The goals and plans of 5-6 iterations of Aaron and Abe are nearly impossible to keep track of, including by the characters themselves. By the time of the "Granger Incident", they can't even be sure that they aren't part of gambits involving iterations of themselves which we never even see.
Down with Love: Catcher assumes a false identity in order to trick Barbara into falling in love with him so that he can publicly discredit her. Just when he thinks he's succeeded, she pulls the rug out from under him by revealing that she knew who he really was the whole time, and she was also operating under a false identity to make him fall in love with her. Ironically, her plan worked splendidly, but caused her to fall out of love with him, so that he has to try a completely new strategy in order to win her back.
House of Flying Daggers is a tangled web of intrigue in which pretty much everyone is found to be secretly deceiving or plotting against pretty much everyone else.
The plot of Get Shorty rapidly escalates into a Gambit Pileup, and remains one until the final resolution; that's really the whole appeal of the movie, unless you'd enjoy an Affectionate Parody of Hollywood.
Wild Things, with reveal after reveal, every character shown to betray and kill their erstwhile allies for the benefit of some other ally, who in turn betrays and kills them, and so on. Every sequel strives to escalate to make each plot twenty times more convoluted and confusing than the previous film's. Chances are, if you are the protagonist, the antagonist, the victim, a background character... hell, if you're in the film, you are in on the scheme and may be weaving some incredibly complex plans of your own.
Sleuth is a play adapted into a movie with only a few characters. The main characters continually play with each other, psyching the others out mercilessly.
Duplicity pretty much devolves into this. Their primary gambit requires an increasing number of sub-gambits all of which are rendered moot by Howard Tully's Batman Gambit that trumps them all.
Threatens to happen a couple of times in the Infernal Affairs films, but it really gets out of control in Infernal Affairs II with all the maneuvering among Ngai Hao, Wong, Sam, and Sam's wife Mary.
Maverick has a doozy. Angel's order to keep Maverick away from the big poker tournament turns out to have been sent by The Commodore, but that entire plot is a Red Herring. The real conspiracy is between Cooper and The Commodore, then The Commodore tries to pull You Have Outlived Your Usefulness, but then Cooper and Maverick manage to Out Gambit The Commodore and get away with the money.
There are also quite a few side gambits executed by Maverick, Annabelle, and others both for and against each other just to acquire enough money to enter the tournament.
The Sequel Hook indicates Maverick is already planning a new game just for the fun of getting back the portion of the money that gets stolen from him.
Mission: Impossible Fallout: The plot with the White Widow involves at least six different factions working with and/or against each other, some in multiple ways (the IMF, CIA, MI6, the Apostles, White Widow's brokers, and the unknown assailants trying to kill John Lark). It's not quite clear in retrospect how each groups' actions were supposed to further their plans.
Takers has this trope in spades, as there's several gambits that all end up in a very messy collision at the end.
Equilibrium wherein the ruling evil empire causes their best agent to be corrupted so he can lead them to the leader of the noble rebels who allow themselves to be captured and executed because somehow they know that is the only way he will be able to see the leader of the evil empire in person.
The hapless main characters in Strange Days find themselves dragged into the chaotic aftermath of what happens when several would-be master plans have already started crashing into each other and spiraling way out of control.
The club shootout in Collateral devolves into one, in which six different factions are involved, all with wildly varying interests. The Feds think Max is Vincent, and try to arrest him while escorting Lin (Vincent's target) safely out of the building. LAPD Detective Ray Fanning knows something is up and that the Feds are acting prematurely, and tries to help Max. Max just wants to get through the whole thing alive, and also prevent Vincent from killing his mother if he fails. Vincent wants to kill Lin, while using Max as a decoy. Lin's security guards are just trying to protect their boss, are startled by the Feds rushing in with guns, and turn the thing into a shooting spree to start with. Felix's guards also think Max is Vincent, and will kill him if things go wrong. Vincent comes out on top. The Feds are rendered useless by Lins bodyguards, Felix's guards are scared off by Vincent, he kills both Lin and his bodyguards, kills Ray after Ray just escorted Max out of the building, and forces Max to continue driving him to his next target.
L.A. Confidential involves four different cop's plans with wildly different motivations, and some other characters that take different parts in these four plans. Even those going for the crime control have different plans and betray each other.
The Damned (1969) has each member of a German steel family scheming to take over the company and curry favor with the Nazis. Murder, blackmail, backstabbing and other shenanigans ensue with increasingly convoluted results.
The Thieves starts as an attempt to heist a diamond from a casino. However, almost everyone involved has an agenda of their own and an elaborate series of double and triple crosses ensues.
The western comedy The Great Bank Robbery features four different groups all simultaneously targeting the same criminal-operated bank in 1880's Texas.
Just about every major character in Circus has some sort of scheme running: Leo, Lily, Bruno, Caspar, Julius, Troy, Elmo, and even Gloria (after a fashion). All of them come crashing together as the film races toward the conclusion.
The plot of Knives Out is driven by three conflicting gambits which are finally unraveled at the end. Ransom attempting to disinherit Marta by tampering with her medicine bag and misleading her afterward; Harlan trying to protect Marta and her family with a plan carried out by Marta; and Fran trying to blackmail Ransom for killing Harlan.