Sixth Ranger Traitors in Video Games.
- Khunag of Albion joins the party as the sixth ranger. He has little role for awhile. Then at one point, the player must infiltrate the cult he once belonged to, and he's the only guide available. He 'guides' the player into declaring war on the cult, slaughtering their best warriors and eventually killing the leader, with whom he had a score to settle.
- In Another Day, the bonus chapter of The World Ends with You, Rhyme, of all people note pulls this on Neku...er, Shuto's team of Tin Pin Slammer-playing heroes.
- Subverted in NEO: The World Ends with You with Shoka. Originally joining the Wicked Twisters as a mole to spy on them for the Reapers' benefit, she felt incredibly guilty betraying her now teammates who considered her a friend. She ends up fully defecting from the Reapers and permanently joining the Wicked Twisters as a proper Sixth Ranger.
- In Baldur's Gate II: Shadows of Amn, your starting party consists of entirely of characters from the first game... and Yoshimo. Guess who betrays you?
- Onef of The Banner Saga. Is recruited from Frostvellr, and fills out this role in the party. Invariably turns on the party later on, as pointed out by their class title "Backbiter". Ends up killing a good number of your clansmen along with Egil, and Oddleif comes scarily close to dying as well.
- Harle in Chrono Cross, twice, betraying Lynx for you because you are Lynx and then betraying you for the Dragons after you beat FATE.
- Final Fantasy series:
- In Final Fantasy IV, when returning to Baron, you run into the captain of the Baron guards, Baigan. He "joins" your party (despite the fact that your party is already full; the game doesn't allow six playable characters to be used at once) and he follows along behind you (unlike all the other party members who aren't shown on screen during normal gameplay). He is revealed as a monster in disguise about five seconds later. In the DS remake, this is played as a cutscene and Baigan has a new 3D model, and he immediately reveals himself as a monster in the cutscene.
- Final Fantasy X - Maester Seymour, since he joins the party briefly before turning out to be an Omnicidal Maniac.
- Final Fantasy XII offers one for both sides: The heroes get Vossler, and the villains get Gabranth.
- Final Fantasy Tactics gives us Algus/Argath, the guest for about half of Chapter 1. Also Gafgarion, a guest for several battles during Chapter 2.
- Final Fantasy Tactics A2 gives us Adelle, though she's merely Brainwashed and Crazy.
- Played with in Fire Emblem Fates. The Avatar unintentionally becomes one in the Conquest version of the game when they return to their adopted family in Nohr after being reunited with and fighting alongside their biological one in Hoshido for a while.
- Fire Emblem: Three Houses has a sympathetic example on the Crimson Flower route in Flayn. She is a late joiner to the Black Eagles, but deserts them if they decide to follow Edelgard and declare war on the Church of Seiros.
- Aydana Kozlova in Ghost Recon: Shadow Wars is a subversion of this trope. She seemed to betray the team and released the enemy that The Squad had just captured. It turns out that she only released him so the team would be able to track him down and lead them to the Big Bad. Then she rejoined your team and was Easily Forgiven.
- Grim Fandango: Shortly after joining the LSA, Olivia betrays Manny and the rest of the group for her new boyfriend, Hector LeMans.
- Dark Pit from Kid Icarus: Uprising was created by Pandora to be an Evil Knockoff of Pit who'll fight for the Underworld Army. 10 seconds after his creation, he defects and becomes a neutral Wild Card during most of the game until he joins with Pit near the end of the game.
- This is all due to Dark Pit being Pit's opposite. But rather than morality, Pit's core virtue is his loyalty.
- Mass Effect 3: Maya Brooks in the "Citadel" DLC. She pretends to be a low level, bumbling but well-intentioned Staff Analyst, helping to uncover the assassin who is attempting to kill Shepard by providing the team with dossiers, information, and advice. In actuality, she is behind the attempt, intending to kill Shepard and replace them with a clone that will allow her to use Shepard's connections and reputation to push her Human Supremacist agenda on the galaxy.
- Onmyōji: Yaobikuni, who suddenly turns on her friends and reveals her motives after being taken to Kuro Seimei's place. She is still a playable character after this revelation.
- Goro Akechi in Persona 5. Subverted in that the gang already knew he was The Mole from the start and actually finds a way to counter his plan (to kill Joker and have the Phantom Thieves arrested) with a very clever Batman Gambit. He later joins the party for real in the Royal Updated Re-release. There's also Yoshizawa, who briefly turns on the party during a Heroic BSoD before coming to her senses.
- Phantasy Star IV has "Seth" who you meet at the entrance of a dungeon. At the end of said dungeon, he turns out to be the third incarnation of Dark Force that you fight in the game.
- At the end of Planescape: Torment, depending on your alignment either the Token Evil Teammate Ignus or the insane Sixth Ranger Vhailor will turn on you at the behest of the Big Bad in the final dungeon.
- Ratchet & Clank Future: Tools of Destruction: Rusty Pete only allies himself with Ratchet to find the body of Angstrom Darkwater so that he can revive Captain Slag.
- Courtney Gears in Ratchet & Clank: Up Your Arsenal. At first, it looks like she agrees to assist the Q-Force in helping out with their battle against Dr. Nefarious, but soon betrays the team by kidnapping Clank and using Skidd as a test subject for the Biobliterator in her lair, the Obani Draco. She soon meets her end at the hands of Ratchet, but is later restored.
- Saints Row (2022) has the Nahualli, who is the Starter Villain in the first mission, then later gets broken out of prison in order to have him help the Saints out on a Train Job. He's integrated into the gang, tagging along on a team-building activity day, and seems to have become a loyal new member of the Saints, but at the game's climax, he betrays the Boss out of jealousy for their friendship with Neenah, Kevin, and Eli and ends up becoming the Final Boss of the game.
- Penelope in Sly 3: Honor Among Thieves is technically the second recruit, and therefore the fifth ranger, but the way she joins is different from the Guru, Panda King, and Dimitri; they all join out of gratitude for the Cooper Gang's help with their own problems, while Penelope joined to keep her promise to Bentley. Nobody knew she had a very selfish motivation for joining until it was too late, and she betrayed the gang to Le Paradox in Sly Cooper: Thieves in Time in order to harvest Bentley's "potential" and Take Over the World.
- Applicable to two different character routes in Star Wars: The Old Republic.
- The Republic Trooper story inverts the trope, casting the player character as the newest member but being the only one squad member to remain loyal after everyone else defects to the Empire.
- The Imperial Agent story plays this straight and has this happen twice over; the player character themselves serves as one for a team of Republic spies, acting as a double-agent to get info - only for another member of the team to be a double-agent themselves, except that they serve a third group who is inflaming the war for their own ends.
- The only playable character in Tales of Xillia 2 not previously established from the first game is the protagonist Ludger Kresnik, who in the Bad Ending kills the rest of the party in order to stop them from sacrificing his brother.
- Ultima V has Saduj who can join your party, but it turns out he's a spy for the Big Bad, not just that but he'll flee every battle you enter massively dropping your karma eventually making the game unwinnable. Really the only use for him (Without him having to join) is that he's the only clue to the existence of the Sandalwood Box that is one of many items you need to beat the game, and that you can make him a Hairu in a particular battle.
