13 Sins: It's implied that a large number of people are involved in the game, including people high up in authority. Det. Chilcoat seems to be a reasonable authority figure, trying to figure out the game. He's actually their cleanup guy.
Fay in Adopting Terror, is feeding information to the biological father who's terrorizing the adoptive family.
Air Force One has Agent Gibbs, a traitorous Secret Service agent who helps Ivan Korshunov and his group of terrorists access the weapons to take over the titular plane. Gibbs proceeds to play dumb for the rest of the film until the plane has to be abandoned, whereupon he shows his true colors to President Marshall to save himself.
A One Nation Earth officer in the Apocalypse film series movie Tribulation shows up in a Christian hideout ready to kill all the Christians in it, but as it turns out only fires blanks, revealing himself to be on their side.
Big Game has two: Morris disables Air Force One's self-defense systems, allowing Hazar to take it down, and Herbert texts Hazar when situation deteriorates to the point the president must be killed instead of taken alive.
In Black Christmas (2019), Helena apparently believes in the frat's stance on the position of women, and acts a mole inside the sorority: stealing the items the frat uses to track their victims.
Braveheart played with this trope and its variants; when two characters join Wallace's crew, one appears to be the mole but it turns out to be the other one and the first one saves the hero.
The prisoners in Breathing Room soon realize that one of them must be feeding information to their captors. It's Number 14.
Bunni: Chris is revealed to be working with the killer, aka, his mom.
Captive State: Mulligan turns out to be one in the government for the Resistance.
There are two in Carlito's Way. One is revealed right away and is working for the FBI, the other is not revealed until the ending.
In Chai Lai Angels: Dangerous Flowers, the Big Bad Dragon cannot figure how the Chai Lais always manage to turn up in time to thwart his schemes. At the end of the film, the Chai Lais handler reveals that he had a spy planted in Dragan's oragnisation. It's Katherine.
The Departed is the story of a mole in the Massachusetts State Police and another in the Boston Mafia trying to discover each other.
At one point the mole is tasked at trying to find the mole in within the State Police, Himself. He wasn't the only mole; unbeknownst to him until the very end.
Which is a remake of Infernal Affairs, where the mole was in the Hong Kong police and the other mole was in the Triads.
Die Another Day: Miranda Frost betrays James Bond and MI6 after Graves bought her out with an Olympic gold medal.
In Disraeli, the Russians have a mole in the office of Prime Minister Benjamin Disraeli. Disraeli knows this, and uses the situation to his advantage.
Dog Soldiers had a mole, who didn't intend to be the mole originally. The one woman who rescued the soldiers from the Werewolves and tries to help them escape from the surrounded country house is revealed to be a member of the Werewolf family herself. Apparently, it seemed she thought the soldiers knew about the beasts and had come to rescue her (and perhaps cure her) from the Werewolves. However after every escape plan goes wrong, she reveals herself to be one of them, reveals that she had let the rest of the wolves in the house while they were busy and begins changing into one of them herself.
Headhunters shows Ove as an employee of a security company who was specifically planted to deactivate alarms for his art burglar friend.
In The Heat, Adam, the DEA agent, was Larkin all along.
In the fourth Home Alone film, Kevin suspects that the burglars have an inside man who is helping them with the kidnapping and believes it to be Mr. Prescott. He is surprisingly right, although it turns out to be the maid Molly, who is also Marv's mother.
House of Flying Daggers: Jin pretends to go to the good side before going for an actual HeelFace Turn, but everybody thinks that he's still working for the government. Then we find that Leo, who set up Jin's finding out where the Flying Daggers were, is actually one of the Flying Daggers and was a mole.
"So what, you're a triple agent?" "No, I just lied about being a double."
In Indiana Jones and the Last Crusade, Dr. Elsa Schneider is revealed to be working with the Nazis about halfway through the film. She pretended to help Indy in order to obtain Henry Sr.'s grail diary, which could confirm the location of the Grail's resting place. Elsa, however, subverts her role when she purposefully gives Donovan the wrong grail, which eliminates him from the picture, allowing Indy to obtain the true grail and heal his father. In the end, this (questionable) redemption is not enough, as she tries to leave with the grail from the temple. In a Take My Hand! moment, she can't keep herself from reaching for the grail below her as she hangs on to Indy above a deep abyss. She ultimately loses her life when her gloved hand slips away and she falls to her death.
In Ip Man 2, "Fatso" appears to be a minion of the brutal British at first, until he turns out to be working for their arrest. Foreshadowed by his offering to silence editor-in-chief Kan, then not doing so after the British policeman leaves.
Dr. No. Miss Taro is an agent of Dr. No who works as a secretary in Government House, passing classified information on to him.
In both Casino Royale (2006) and Quantum of Solace, an Illuminati-esquecrime syndicate known only as "Quantum" has its operatives planted within many governments and corporations as a way to secretly dominate the world and tilt events to its favor. They've even managed to penetrate MI6, CIA and even the Canadian and Russian intelligence services. For example, the Big Bad of Quantum of Solace, Dominic Greene, for instance, is the head of a Greenpeace-style organization that is actually in business with a lot of shady corporations and criminals. In Spectre, it's later revealed that SPECTRE and its leader Ernst Stavro Blofeld is the one behind the villains of Casino Royale (2006) and Quantum of Solace, and even bankrolled Raoul Silva's schemes in Skyfall. Blofeld's Evil Plan is to seize control of the world's major intelligence agencies through a series of staged terrorist attacks, and the data would then be forwarded to him via his moles, including Max Denbigh, the head of the merged MI5 and MI6.
In The Last Witch Hunter, 37th Dolan turns out to have infiltrated the Axe and Cross to aid the Witch Queen's supporters.
Paul Blart: Mall Cop: Paul Blart's trainee Veck Sims is the main villain. The trainee is the brainy.
Mannequin: Richards (played by James Spader of The Blacklist). Yes, a plant for a rival department store seeking to buy out the one he is infiltrating.
In the movie adaptation of Mission: Impossible, the team leader Jim Phelps, essentially reversing his portrayal for the entire run of the original and second series.
The Negotiator: Commander Grant Frost is the one orchestrating the whole scheme that stole money from the orphan fund, murdered Danny Roman's partner Nathan Roenick when he found out, and framed Roman for it.
No Way Out features a remarkable combination of a mole and a Red Herring Mole. The murder of the mistress (Sean Young) to the Secretary of Defense (Gene Hackman) is blamed on a Soviet mole as a Red Herring to divert attention from the real killer (the Secretary himself). The protagonist (Kevin Costner) must race to find evidence of this before they figure out that he's the one being framed. The twist is that although he didn't kill the girl, Costner really is a Soviet mole.
In The Phenix City Story, Jeb Bassett, one of the Pattersons' associates, secretly reports to mob boss Rhett Tanner.
Reservoir Dogs. After a heist goes wrong, the main characters become paranoid, with Mr Pink repeatedly claiming there has to be a mole. We eventually discover it was Mr Orange.
In Resident Evil: The Final Chapter, the Red Queen warns Alice that there's an Umbrella agent amongst the group helping her infiltrate the Hive. It turns out to be Doc, which Alice has already figured out by the time it's revealed, since they're the only one of the group other than her and Claire who's still alive.
The Adventures of Rocky & Bullwinkle parodies this trope's name. The villains have a mole in the U.S. government that allows them to get information about what the government is doing. The mole is revealed to be a literal mole that is part of the President's Staff.
One of the people in Rōnin is not actually "Rōnin", and is still working for his/her agency. It's Sam.
In Running Scared, the two protagonists seem about ready to be gunned down by gangsters fairly early in. Lo and behold, two of the bad guy'sMooks turn out to be undercover cops and rescue them.
Andy, in Shuttle, appears to be one of the passengers held hostage by The Driver, but is actually his conspirator, which comes in handy when the heroes get the upper hand.
Shot Caller: Shotgun is working with Officer Kutcher to bring down Jacob and the rest of the Aryan Brotherhood, since his drug-smuggling girlfriend has a twenty year sentence hanging over her head. Jacob kills him when he finds out.
Becky in Sin City ends up ratting the Old Town girls out to the mob.
In Sisters of Death, Mr. Clyburn tells the girls that one of them knew for sure that the hazing ritual that killed his daughter seven years ago was sabotaged, and that that witness was working with him. It was Sylvia, who actually pulled the trigger in the ritual
Soldier of Orange: Robby sold out his friends to the Germans and lured them into a trap during the beach operation. He's later assassinated by Guus, who is himself arrested in the process.
In Spy, Karen Walker turns out to be one. Bradley, meanwhile, reveals himself to be a mole for Rayna, but is actually a mole for the CIA.
The director of intelligence in Starship Troopers 3: Marauder is initially seen by one of the protagonists (and the audience) as a traitor who's trying to assassinate the Sky Marshal, covering up the failed attempt and preventing his rescue, and seizing power. Well, she actually is doing all that...because the Sky Marshal has gone nutty (well, nuttier) and is going to sell humanity out to the enemy.
The Rise of Skywalker: General Hux is concerned enough over Rens influence over the Dark Side that he aids the Resistance in infiltrating a key First Order starship, without fully turning over to their side.
Stalag 17 involves one of these in a German POW camp during WW2. It turns out to be someone other than who everyone assumes it to be.
In The Thieves, Julie is planted on the team by the Hong Kong Police to lead them to the reclusive fence Wei Hong. Interesting her father really is a notorious thief, the reason that the undercover role was so easily believed.
Wild Wind has an American spy impersonate a Nazi collaborator.
In The Windmill Massacre, coach driver Abe is actually an agent of the Miller, delivering souls to him, and referring to him as "Master".