In One Piece arcs, this happens very frequently, usually when the Straw Hats are breaking into their destination. In the Alabasta arc, the crew splits up to act as decoys to engage the Baroque Works Officer Agents so that Vivi can stop the rebellion. In the Skypiea arc, they split into two groups- one to find the gold and one to get the Merry to a place where the gold team can meet it to escape, but as a result of a variety of happenings related to the Survival Game (like Eneru attacking the Merry and a snake causing the gold team to get separated), this doesn't work out as they expect and the crew ends up separated until the climax. In the Enies Lobby arc, the crew is forced to split up to fight the CP9 agents who hold the keys to Robin's handcuffs. In the Sabaody Archipelago Arc, Luffy has his crew split up when the enemies that arrive prove too strong for them, but after Kizaru cuts off their escape, Kuma appears and sends all the Straw Hats to separate islands.
Anime episode #150 (Season 7, Hueco Mundo Sneak Entry). Ichigo, Rukia, Uryu, Chad and Renji are in Las Noches and facing 5 doors that might lead to Orihime. Rukia suggests that each member of the party go through a separate door, and they do. Uryu ends up finding Renji and getting involved in his battle agains Szyael, while Ichigo ends up being the one to find Orihime.
The New Captain Shūsuke Amagai arc (season 9). Suggested by Ichigo while hunting for assassins in Karakura Town.
In season 2 of Digimon Adventure, they go around the world in this manner, dealing with the global outbreak of Digimon appearances (Subverted somewhat in that each group teams up with regional Digidestined).
Fullmetal Alchemist: In Episode 19 of Brotherhood, Mustang splits the group at a junction to make finding Barry the Chopper easier. It doesn't turn out too well...
In HeartCatch Pretty Cure!, the team splits up, dealing with a different threat (Cure Marine against Kumojacky, Cure Sunshine against Cobraja and Cure Moonlight against the Dark Precure), to allow Cure Blossom to rescue her grandmother.
Justified again in the third chapter, where only one Blue Suns hovercar out of five is sent to investigate the car left behind by the team and where Courier is lurking: they donít expect him to stick around near the facility and so the rest are searching for him on the outskirts.
When Steed and Mrs. Peel first go to Sir August's estate, Mrs. Peel distracts him while Steed snoops around the grounds.
While Steed and Mrs. Peel are pursuing the two people dressed as bears in the Wonderland Weather building.
As Steed, Mrs. Peel and Alice infiltrate Sir August's estate, Alice suggests that they split up while going through a maze. This allows Mrs. Peel to fall into a pit trap and be captured and Steed to be knocked out by Mrs. Peel's Evil Twin clone. Good idea, Alice!
After Alice wakes up Steed in the maze, they split up again to find and rescue Mrs. Peel.
In Sir August's underground lair, Mrs. Peel goes to disarm the weather control device while Steed seeks out and fights Sir August.
Ghostbusters. The title characters are looking for a ghost in a hotel.
Ray: I think we better split up. Egon: Good idea. Peter: Yeah, we can do more damage that way.
A large part of the premise and conflict in the second act of the film Clue. Specifically they split into pairs. There's even a kind of logic to it, as Col. Mustard points out: if one half of a pair winds up dead, then the other half is probably the murderer.
Sky Captain and the World of Tomorrow. While in Dr. Totenkopf's abandoned uranium mine, the title character says "We'll have to split up." Little does he know that Polly Perkins has already wandered off on her own.
In Star Wars Episode III: Revenge of the Sith, Yoda and Obi-Wan split up in order to kill the two evil Sith Lords. Ultimately, neither is successful, but come within a hair's breadth of being so.
Tank Girl. Tank Girl and Jet Girl when they enter Liquid Silver.
Monty Python and the Holy Grail. King Arthur and his knights split up in their search for the holy grail after failing in their assault on the French castle.
HISTORIAN: Defeat at the castle seems to have utterly disheartened King Arthur. The ferocity of the French taunting took him completely by surprise, and Arthur became convinced that a new strategy was required if the quest for the Holy Grail were to be brought to a successful conclusion. Arthur, having consulted his closest knights, decided that they should separate, and search for the Grail individually.
Starship Troopers: Rico gets a feeling that Carmen is down a separate tunnel than the one his platoon has been ordered to explore. Knowing the severe penalties for disobeying orders during a battle (what he's doing could be considered desertion, not to mention abandoning his command), he places the platoon under a subordinate's command, takes a small handful of volunteers (coincidentally the entire surviving main cast) and goes off on his rescue mission after Carmen.
Danny Boyles's Sunshine: Subverted, could also seem like "Genre Savvy":
Mace: We should split up. Harvey: I'm not sure that's such a good idea... Mace: You're probably right. We might get picked off one at a time by aliens.
Brenda: Uh uh uh uh uh uh uh uh UH! Now wait a minute, hold up! How come when anytime this scary shit happens, and we should stick together, you white people always say "let's split up"?
Theo: She's right, we should stick together.
Dwight: She's right. Okay.
[points to the white people in the group]
Dwight Hartman: You three, follow me!
[the three black people are left alone]
Shorty: Ain't that a bitch.
[the three of them begin to cry]
Brenda: We gonna die, y'all.
Fright Night. While Charley Brewster and Peter Vincent are looking for the vampire's coffin in the basement they hear a noise. Charley tells Peter to continue looking for the coffin while he checks out the noise. This results in Charley confronting a vampire by himself and almost being killed.
In Crouching Tiger, Hidden Dragon, the two main characters split up: one goes to find the Big Bad while the other hides the MacGuffin. This is lampshaded in the commentary section of the DVD where one of the writers jokes that they made a classic horror-movie mistake.
In The Cabin in the Woods, when the Main Characters start being hunted by monsters, their first instinct is to stick together no matter what. However, thanks to subliminal messages and intelligence-dampening drugs, the puppeteers behind the situation get the characters thinking they need to split up. The Only Sane Man in the group is completely befuddled by this.
In the New Testament, the original Apostles split up after Jesus' ascention to carry his teachings into different countries. Canonically, except for the Council of Jerusalem, they never meet up again in Real Life, but according to the Word of Dante (literally), they all eventually come together again in Heaven.
In Starship Troopers, while exploring a Bug Hive, the narrator mentions that the prescribed MI battle doctrine is to leave 10% of your force behind to cover any forks in the tunnel, rather than splitting your force up in two to explore the tunnels separately, with the added bonus of them making sure the bugs don't sneak up behind you. Rico decides that this would be an excellent way to end up with him at the deepest part of the tunnel with a very small handful of troopers, and instead decides to leave only two troopers to cover each junction, giving him a bigger force to use in the deeper, more dangerous parts of the tunnels.
Happens during the Quarter Quell in Catching Fire. It does not end well.
Played absolutely straight in Ghost Story by Peter Straub. Heroes enter evil house, decide they need to split up for very minor reasons, and things go badly. A tiny lampshade is hung, but it's still idiotic.
Resisted by Anya at the beginning of season 6 ("No — bad idea!"), but the gang splits up anyway.
Lampshaded by Willow in the season 1 episode "Nightmares":
Xander: Probably faster if we split up to look for her. Giles: Good idea. He and Xander go off in opposite directions. Willow: Oh, uh, faster, but... not really safer.
Buffy: This'll probably go faster if we split up. Anne: Can I come with you? Buffy: ...OK, where did I lose you on the whole splitting up thing?
Lampshaded by Rimmer (natch) in the Red Dwarf episode DNA:
Lister: Okay, look, let's split up. Rimmer: Why? Why should we split up? Lister: Well, we'll do the search quicker. Rimmer: What's the hurry? Have you got some major luncheon appointment you have to rush off to?
Lampshaded by Daniel Jackson in the Stargate SG-1 episode "The Tomb":
Maj. Vallarin: Wait here. Jackson: Yes, you go down the dark hallway, alone, and I'll wait here in a dark room, alone.
Smallville. In "Supergirl", when Clark and Kara enter the S&M club Clark suggests splitting up so they can cover more ground.
In Power Rangers Operation Overdrive, when the Rangers do this, Dax says that this is just like the part in a horror movie where everyone splits up and gets picked off one by one. Nobody listens to him. (They don't get picked off one by one, but one Ranger does get kidnapped.)
Goes back to the original: The Green Ranger storyline had Tommy kidnap Jason at one point, then defeat both sides. Later, during the green candle episodes, the party was again split, with Tommy fighting a monster and Jason trying to capture the eponymous candle.
The Daleks, the second serial of the original run of Doctor Who, had this in the first episode, The Dead Planet:
Ian: Why don't we seperate and go different ways and meet back here in ... say ... ten minutes, alright? Barbara: Alright, I'll go this way. Barbara goes down one corridor, Ian another and the Doctor and Susan take the third. Less than five minutes later the angriest pepperpots in the entire history of time and space make their television debut.
In the Second Doctor story "The Faceless Ones," the Doctor and has three companions arrive on the tarmac at Gatwick Airport. When it looks like they're about the be apprehended by authorities, the Doctor's reaction is to call out, "Scatter!" And they did, and his companions all went off and very nearly got killed...in different, equally perilous situations.
And numerous further examples over the following decades have led to "companions wandering off and getting in trouble" being firmly established as a DW cliche.
This happens on Misfits when the group are trying to track down a malevolent shapeshifter - a pretty foolish decision given that she can, y'know, shapeshift to resemble any of them. To their credit, they did devise a password so they could identify each other, and the plan might have been effective had Nathan not screwed things up quite so royally.
In one of the more commonly cited episodes of Criminal Minds, The Big Game, Reid becomes excited about an epiphany he's had and tells JJ, who he's with, that they should split up. She weakly protests but complies anyway, and it all goes to hell from there. The stupidity of their actions is lampshaded in a later episode when JJ says to Reid, "No matter what happens this time, we don't split up, clear?"
Happens in Heroes during the volume 3 finale episode "Dual". Sylar locks Claire, Meredith, Angela, and HRG in with him at Primatech because he's a bit pissed off about Angela lying to him and saying that she's his mother. Sylar also had some good reasons to be pissed at HRG too, such as HRG and Elle helping to make him into the monster that he is now. Everyone decided that the best way to deal with the over-powered serial killer is to split up. Needless to say, it didn't end well, at least not for Meredith and those two Level Five guys.
Lampshaded in Malcolm in the Middle when Malcolm, Reese, Dewey, and Stevie end up alone at an abandoned carnival after dark:
Malcolm:(to the camera) This is like the beginning of every horror movie I've ever seen.
Dungeons & Dragons 1st Edition module I10 Ravenloft II: The House on Gryphon Hill. While the PCs are at the Weathermay estate, the NPCs there will offer to help them. If any of the NPCs have been transposessed by an undead they will suggest splitting up the PC party and NPCs to search the grounds more quickly. If the PCs are foolish enough to agree they can expect to be subject of a Total Party Kill at the hands of the numerous undead and other monsters swarming around.
In the Tower of Mana, the party leaves half the party on the switches in the lobby and takes the rest through a door. In the Palmacosta Ranch, the player forms two parties, as a result of needing to deactivate the security at the end fo the ranch where the prisoners are being kept to reach Kvar. In the Iselia ranch, the player forms two groups- one to rescue the prisoners and one to stop the reactor, because they are short on time due to the Great Seed going out of control, and the player does not control the party that frees the prisoners.
Also in Tales of Vesperia. In this game, you could pretty much count on splitting up each and every time you entered a town to advance the plot. Occasionally done to force you to have a quick chat with each party member before the plot actually went anywhere, as a form of Character Development.
Happens once voluntarily in Tales of the Abyss, at which time you get to choose which characters to take (for plot reasons, Jade has to go to Engeve and Natalia to Kaitzur at the same time, and you get to pick where the others go), and once involuntarily, in which case the pairings are chosen for you by the plot.
A somewhat odd occurrence happens in Final Fantasy V. There's a portion requiring two teams, but there's no spare party members waiting around in this game. This means not having to deal with underlevelled characters that one can't equip, but gives you a pair of parties that are only half-manned instead.
Don't forget that one half of the tower forbids you from casting magic while the other half has enemies only vulnerable to magic.
Several times in Final Fantasy VI. The final dungeon in fact requires three teams to get through. The ability to switch between them at any time lets you park one group on a save spot and lets you save at any time as the other party moves up.
In Final Fantasy VII after escaping Midgar, Cloud suggests splitting the team into two traveling groups and then meeting at Kalm later. This is an amusing subversion in that the expected two plotline trip just ends up being a tutorial for party switching and nothing more.
On the other hand, the final dungeon in Final Fantasy VII does require splitting up your party, and even the penultimate boss can be fought with multiple parties.
Storywise the party does travel in separate groups until you acquire the Highwind midway through Disc 2. Until then the entire party showing up in a location is a hint that something big is about to go down soon.
Similarly, the final dungeon of Final Fantasy VIII requires two teams of three to act independently to solve many puzzles.
Also happens at other points in Final Fantasy VIII, where, for some, the main worry was having enough GFs to junction the entire team.
However, it was possible to transfer GFs and junctions between party members even if the sending character wasn't available. You just had to remember this every time you had to switch...
Final Fantasy IX simply let you choose three party members to go with Zidane on one quest, and then take control of the other four as they battle through a dungeon. The next time you split up into four pairs only in the story sense, as you only control Zidane/Quina.
The entire first third or so of the game is like this, with all the party members together, then splitting up on their own individual sidequests, before they finally reunite in Disk 2. At that point, however, some of the characters are Put on a Bus, leaving enough room for the last party members to meet the Arbitrary Headcount Limit. When the whole party reunites at the start of Disk 3, they never split up again, except for the previously mentioned example.
Happens once in Final Fantasy X. When the party is sentenced to death in the Via Purifico, Tidus, Wakka, and Rikku end up in the water (rather conveniently, as they are the three party members that can fight underwater) which leads up to a hilariously easy redux of the game's That One Boss, while the rest of your party has to navigate a land-based labyrinth.
Final Fantasy XIII does it for the first half of the game. At first, the five original party members are split up. They come together for a while, just in time to receive their magic powers together. A short walk later, one stays back to protect his girlfriend. The other four manage one Boss Battle together before going their seperate ways over a difference in opinion over their Focus. The guy who staid back is then met by the sixth party member, who meet up with one of the pairs, only to switch partners but remain split up. When they finally manage to get together, they then go to rescue the last pair who got captured. Control bounces around the groups so you get to play all of them. Basically, as a result of this, you can't actually pick your party members until roughly 3/4 of the way through chapter 9 (of 13).
Final Fantasy: The 4 Heroes of Light: the eponymous four heroes split into two groups after a staggering, ooh, one battle together, with half staying together to figure out the source of the curse on Horne, the others going to Liberte. Then they split further, with heroes blundering off alone due to impatience, guilt, or good old-fashioned stupidity. One character gets left behind by someone skulking out of the inn early in the morning, two towns in a row.
Happens once in Shadow Hearts, with the added twist of the individual paths being tailored to exploit the weaknesses of each group. For example, the group which includes your most potent mage has to traverse an anti-magic dungeon.
In Covenant, the party has to split up in order to get through the Mikasa Warship...with two security keys.
In Xenosaga Episode I, The gang splits into two in the Encephalon. This comes as a major shock to players who have been neglecting certain characters.
The original Knights of the Old Republic had a sequence in which you must choose a party member to go rescue the main character and his/her two potential love interests, and Jade Empire features several such sequences, mostly during the end game.
Mass Effect 1 would appear to be the exception. You're never limited in your choice of party if they're still alive, and at least one will be dead by the end of the game and they stick to you like glue up to and including the final showdown with the Big Bad.
Mass Effect 2, on the other hand, makes extensive use of this trope. During the final mission, you split into three groups (two strike teams plus a tech specialist), meet up halfway through, split up again (diversion team and strike team with a biotic specialist), only to meet up one more time before splitting up so your crew can Hold the Line, while you fight the Final Boss. And it can either go horribly wrong as per the stereotype, or turn outbrilliantly, depending on who leads which team.
Also, earlier in the game, you are forced to load every crew member who can fight onto a shuttle to go on some ill-defined mission, leaving Joker to fend for himself as the rest of the crew are abducted by the Collectors.
Also in Dragon Age: Origins, there's a part were the protagonist is captured, and you're presented with two options: Break out yourself, or select two companions to control and break you out in The Infiltration. Choosing the latter will lead to several of the funniest moments in the game, like Oghren and Sten's circus act, as well as every other bluffing attempt.
While not developed by BioWare, Knights of the Old Republic II had this in spades. In one instance, one path is taken by the player and two mandatory party members, and the other by three party members of the player's choice. At another point, the main character gets kidnapped and must be rescued by two party members of the player's choice. Then there are at least three moments when one predefined party member must win a fight without assistance from the rest of the party; more were planned, but those were cut due to time constraints.
Similarly, in Skies of Arcadia, a forced party split with no more party members than the usual number results in half-manned duos trudging through different sections of the same dungeon. The game makes it harder by not giving you the choice of who to send where, meaning the physical attackers are in one pair, with the magic-casters in the other.
In DragonBall Z: The Legacy of Goku II, the final fight against Cell is waged by Goku and Gohan, but halfway through, your other three characters get Cell Juniors thrown at them. This is a nasty surprise for some players — but they have no excuse for not seeing it coming, as it's exactly what's supposed to happen story-wise.
The Magic Candle lets you make arbitrary subparties. This is mainly a convenience, provided so individual members can work or train while the others explore. But eventually you have to raise a sunken island by pulling three levers at once — in different places around the world. If you've been relying on one or two fighters to carry your team, this is where you'll regret it.
Batman: Arkham Asylum does this with the mook After you take down a mook such that the others all run over to see it, they will inevitably go back to patrolling with "Now split up and find that Bat!"
During Pikmin you can order your Pikmin to split into groups sorted by colour. A more fitting version of this trope is that they can, and will, split up to fight or perform tasks based on the proximity of said tasks and enemies, but only when idle and not following a captain.
In Pikmin 2 the two captains can also split up to beat certain obstacles/perform multiple tasks. With the number of captains upped to four in [[Pikmin3]] it's shown that this is more-or-less the point of the game.
Septerra Core splits your 9 characters into 3 teams in the final dungeon, without letting you choose team members. Conveniently, the characters that hate each other are together, which can make combats much more difficult due to in-fighting. This is also the only time in the game where you can have a party without the main character, Maya.
In Breath of Fire II, players who refused to use Sten and/or Jean got the unpleasant shock of their lives when they had to use those characters alone in certain important stages. Cue much wailing and gnashing of teeth.
Used in Suikoden II for the battle against Luca Blight (the three parties fight him in sequence) and in Suikoden V for the final dungeon. Given that you need to recruit 108 characters in each game, being able to use 18 of them instead of the usual 6 is kind of welcome.
In Mario & Luigi: Superstar Saga, the brothers are often forced to split up, particularly in Joke's End, in which they spend most of the dungeon on separate paths. Similarly, in the sequel, Mario & Luigi: Partners in Time, Baby Mario and Luigi are often separated from their adult selves. Mario and Luigi stick together more in Bowser's Inside Story, the third game—once Mario finds Luigi, they only ever split up when Mario briefly gets kidnapped. However, that game adds Bowser as a third playable character, and he always travels alone (well, sorta).
On the other hand, there is an Escort Mission with Princess Peach in Superstar Saga. Let her wander offscreen and she gets kidnapped instantly.
Happens in Tactics Ogre: The Knight of Lodis, and given the nature of the game it is definitely meant to strike a blow against the players who didn't bother to train multiple characters.
Happens in the final part of Fire Emblem: Radiant Dawn, but because the game split up the characters in the previous parts already, there is little concern about having enough units to go around.
Early into Fire Emblem: Path of Radiance, the party splits into two groups while trying to sneak past enemy lines, a tactic that the characters almost immediately realize is a mistake (thanks a lot, Soren). There's no opportunity to rearrange items in advance, and the splitters take their gear with them; and with no shops available to you for several chapters, you better not have given your sole heal staff to the wrong unit.
Final Fantasy Tactics and Final Fantasy Tactics Advance had at least one or two occasions where the main character is separated from the rest of his party, forcing him to fight alone in a one on one fight, and usually their opponent was absurdly strong.
In fact, the first time this happens, Ramza is paired off against Gafgarion, who you will recall, has strong long range attacks. The only feasible way to beat him (barring excessive Level Grinding before the battle) is to reunite with the party on the other end of the board by raising the portcullis on the city gate. That, and/or you can have mages from the other side support Ramza if he and Gafgarion are close enough to the wall.
Though if Ramza has a high enough jump stat (possible via the Lancer/Dragoon class), he can jump over the 20-foot wall to escape from Gafgarion. Alternatively, sacrifice a slot on the other side of the gate for a Black Chocobo.
Much easier method: use Break/Rend Weapon. Gafgarion is useless without a weapon, only able to punch weakly.
In Advance and A2, "dispatch" missions involve sending off a character to do a mission, and their statistics determine their chance of success. It's possible to send off several members at once on dispatch missions while your main group does missions of its own (which are sometimes necessary to progress the dispatch missions).
There are several instances in the first Wild ARMs game where the party splits up into individual characters, sometimes to allow for Character Development.
At the very end of Wild AR Ms 2, the player must split all their existing characters into 3 parties to fight the final 3 sub-bosses. The stand-out is that one party consists of only 1 member, so if you assign the wrong character to that party, their sub-boss is unbeatably hard, forcing you to restart the whole dungeon all over again.
Wild AR Ms 3 also had this happen at one point. It was because the rest of the group had left Clive behind to get his shit together and then fell into a trap. Clive then plays the role of the Big Damn Hero and rescues them. However, they remain split-up for pretty much the rest of the dungeon, swapping between Clive and the Party to solve switch puzzles.
The original Resident Evil (and 2002's Remake) has a prime example of this in Jill's scenario; Not content with having Chris and Wesker disappear within the first 5 minutes, Jill and Barry decide it's a great idea to split up, despite being stuck in a mansion in the middle of nowhere, in the dark, just after having seen a zombie eating another team-mate (although to be fair this example is something of a plot device more than anything else).
And, of course, Resident Evil 2's A and B games are based entirely upon this trope — when you complete Leon or Claire's A game, you're given a save file which allows you to experience the other's side of the same events as his or her B game, thereby granting you the "true" ending. Averted -partly- in that explosions kept keeping Claire and Leon apart, but this was not always the case.
Lampshaded constantly in-game, with poor Leon growing more and more exasperated that Ada and Claire insist on ditching him when he thinks they should just be working together. This is understandable for Ada who is a spy anyway, but since Claire is constantly harping on Sherry to stay with her, it gets weird when she leaves Leon half-informed most of the time.
Lampshaded in the novel version of the Resident Evil Zero video game. Rebecca, the main star, keeps wondering why the tarnation she keeps sending her allies off.
To elaborate, the let's split up sections were some of the hardest in the game when playing co-op on higher difficulties. Many players played co-op to get through the game on Insane, and the difficulty was reduced by the fact that your human partner could revive you after being killed, unlike your AI teammates. When you were forced to split up, there were no revives, and a single screwup by you or your partner would send you both back to the last checkpoint. This was the only time when it was easier to play without a human teammate, as the AI would never screw up when it wasn't in a position to actually fight near you.
Some of the split-ups were completely arbitrary, also. There was a section where you had to either choose between a hall filled with lasers or a hall filled with buttons that turned off said lasers. But the doorway at the end of the latter was wide open. There was nothing stopping the player from walking away and leaving the other player to die.
The Lord Of The Rings The Third Age has this. Late in the game, your party splits to defend a certain City. The division couldn't be worse: on one team you have the party leader with immunity to fear, huge combo attacks and tons of Hit Points; the devistating Squishy Wizard and the blasty, buffing dwarf. On the other team you have the rogue with no armor and half as many HP as everyone else, the Ranger who does piercing damage which made him useful against goblins and no one else, and the guy with the spear who actually gives enemies Mana when he hits them and has a few permanent buffs that are usually dispelled by enemy casters in the first round. Also, since the latter three are so lame, you probably won't use them any longer that you have to, so they're a good five levels behind everyone else, too.
Further clarification: On one team, you had a warrior with ridiculous combo attacks and party-leadership skills, an elf who was the only one with decent healing, since items either healed half of what she could heal in one go, or were rare, and, to top it off, a Magic Knight of a dwarf who could use insanely powerful fire spells in addition to ridiculously strong defensive buffs and powerful melee attacks. On the other, you had a ranger who had a bunch of debuffing attacks, but low damage, a rogue who had an entire skill tree revolving around stealing stuff (Mana, health, items), weak attacks, low hp, and pathetic equipment (Out of all the characters, she was the least likely get items dropped for), and, finally, the guy with a spear who tries to be a Magic Knight but fails: his melee attacks are typically single-attack with effects that usually help the enemy and magic attacks that only support... and ONLY support (Dispel, deplete enemy mana, transfer mana/health to/from others). Basically, you had a team that ripped open enemies and a team that could barely defeat a group of enemies from 10 levels ago.
Most main dungeons and some overworld parts in Infinite Undiscovery have these. The game even has several characters who can only be used when the party splits, because they are arbitrarily forbidden from being in the same group as the Player Character.
Some boss encounters in World of Warcraft enforce splitting the party or raid to deal with specific threats. Examples would be the Four Horsemen (which need to be separated) and a group of minibosses known as Twilight Drakes that periodically spawn a portal that most of the raid needs to go through to deal with the cause of potentially lethal problems. It's also a good idea to spread out widely in many encounters as to avoid several people getting hit with area-target effects.
Another example would be the Ulduar encounter with Thorim; where some of the raid will have to go into a gauntlet and meet back up with the others to force the boss into the arena. Doing this quickly will initiate Hard Mode.
In the fight with Beth'tilac, a few members must fight her on top of her web while the rest fight down below. However, it is possible to only send a tank and a healer up, and it is possible (albeit difficult) to send no one up at all.
You can issue this command to your teammates in Persona 3, emphasizing exploration (that is, finding exits) over fighting Shadows, or vice versa. It's not very advisable to do this, as every single Shadow in the game tends to be a Demonic Spider and can kill lone teammates easily, there's a fair chance that they'll run into the Reaper, and they'll keep all the money they find in treasure chests (they do give up any consumable items they recover.) At least, you can still heal them via the menu screen as long as they're in the same room as the main character, and you can join in their battles at any point.
Said feature is useful, but only for quickly clearing dungeon sections that are already beneath you in level (which, given the way the game's waypoint system works, is occasionally necessary.) On any level with enemies close to your level, such a strategy is suicide.
Also enforces the Arbitrary Headcount Limit during the final boss fight by requiring any team members that aren't part of your standard four-member party to stay behind to hold off the encroaching mass of Shadows.
Happens a few times in Sonic Chronicles: The Dark Brotherhood. Depending on which bit of the story it is, some characters are locked into particular parties.
Sonic Adventure 2 has this implied in the Final Story with each character doing something to open a pathway for Sonic to make the final journey to where the Core is and stop the descent of ARK.
In Banjo-Tooie, of the Banjo-Kazooie series, one of the most important moves learned in the game is how to split up Banjo and Kazooie.
The last portion of Popful Mail has the heroes doing this when fighting the Overlord and his henchmen. Gaw takes on Morgal, while Tatto fights Necros and Mail deals with the Overlord himself.
Anachronox only allows you to control a maximum of three characters at a time, forcing you to swap characters at a bar where the currently unusued characters presumably wait around getting plastered until you come back. At the end of the game, however, all seven characters must enter the Big Bad's fortress at once. To avoid having to rewrite the interface, the game creates THREE separate parties, two each of three characters, and one of one, between which the player may swap at will. All three parties must act in concert to reach the Final Boss.
The mid-nineties LucasArts adventure game The Dig uses this trope, after Maggie decides to split up from Brink and explore Cocytus after Brink's death, rationalizing that staying together would mean certain death to them as well, and Cocytus is just as alien to both of them. It works out at the start, after Maggie manages to discover an alien library (through an accident that might have gotten Brink killed had he followed along), but the splitup backfires when Maggie gets abducted by a giant spider.
In Lost Odyssey, your party spends almost the entirety of the third disc split up. At the end of the section, you have to fight a boss that reflects all magical attacks. Your party at this point consists entirely of Squishy Wizards.
The Super Robot Wars series often has Route Splits: missions where the group has to split up to deal with simultaneous crises, or where a part of the group has a separate mission, and usually ends up picking up a number of new party members along the way. The player, playing the part of an Original Generation character, will always get the choice of which group they want to join up with. This helps to add replay value to the game, as you can make one choice the first time you play through, then try out the other choice the second time around.
Super Robot Wars Z gives a unique twist on this. After splitting up one half of your party winds up allying with a rogue faction and viewing the other half as enemies. As a result the next time they encounter each other they wind up battling them. The main character selected at the beginning of the game decides which side the player is on. The more rebellious Rand will go with the rogues, while the meeker and more obidient Setsuko will stay will the initial group.
HalfLife 2: Episode 2: Alyx: "Okay Gordon, me and the superpowered Vortigaunt will sit here and watch you climb through the toxic pit while fighting zombies. Hurry up!"
Well, she had been recently impaled and saved with Alternate Dimension Alien Magic, and Gordon is basically the Messiah. Made more forgivable by the fact that she assists you with a sniper rifle for the second half of the segment.
In ICO, any time Ico leaves Yorda alone, Shadow Men may show up to drag Yorda away and cause a Game Over. Nevertheless, a few puzzles can only be completed by the two separating briefly.
Mega Mari Has the two heroes split up before the third stage of Patchouli's castle/library. There's no apparent reason for this, however.
In Rainbow Six, the team is split up in the last four missions; one team goes to Sydney to prevent a bio-terrorism attack on the Olympics, while the other goes to Brazil to capture the people responsible.
In Summoner, there is a part of the plot which requires Flece to act alone. Then it's Flece and Joseph, then Flece, Joseph and Rosalind, then the whole party again. Later there's a point where Jekhar and Rosalind have to fight alone; they're typically the least leveled, so I suggest level grinding here.
In Summoner 2, there are a couple of plotlines which require you to split up the party. You need to split up into pairs to activate switches at one point, and in the final dungeon the party splits up into pre-ordained groups to follow different enemies.
In Corpse Party, the protagonists are split up against their will. They're cast into separate "closed spaces". Part of the plot is figuring out how to reach each other.
In Evolva, you're forced to split your four-men party several times. Level 5 forces you to split it into two groups, as at least one of your Genohunters (and it's recommend two) has to stay watching over a tunnel entrance. In level 6, two Genohunters are initially apart from the others, and in levels 9 and 11 each Genohunter starts on his own.
In the One Piece action game for the Game Boy Advance, Luffy's crew runs ahead of him every time a level starts, just so he's forced to search for them. It's also a form of Bag of Spilling because they're used for special attacks.
The game Sweet Home more or less enforces this as a game mechanic. You have five playable characters who can either work independently of one another or team up, but even then the largest team size is three. While it is usually possible (if a little tedious) to keep everyone together, there are going to be times when splitting up will be required to get through certain areas.
In Gunnerkrigg Court, Antimony left Kat in a pitch-black room, and the readers immediately started scolding her for it. To be fair, she left her personal demon with her. In spite of a brief scare, they both turn out okay.
Tower of God: After Baam's apparent death, Koon decided that it would be best if he and Rachel separated from the group, while the rest would climb faster under the leadership of Ship Leesoo. He does it because he realized that Rachel actually killed Baam, that it wasn't just her plan and that she was his only lead to the rest of the conspiracy. Splitting up also prevented the rest of the team from noticing that Rachel was faking her disability and disbanding.
Done three seperate times in the Workshop Battle Arc.
The Order of the Stick had the title party get split up for a few months. There was much dancing in the streets when they were finally reunited.
Appropriately, the fourth compilation book, which covers this storyline, is called Don't Split the Party.
There was an episode of What's New, Scooby-Doo? where Shaggy once said it. Fred looked stunned, saying "he said the thing I always say". Another episode also parodied this, with Shaggy and Scooby walking off as soon as Fred suggested splitting up; when he said he didn't say who'd go with who, Shaggy countered with "Like, do we ever do it any other way?" And another episode had Fred deciding to "mix things up"; he went with Shaggy and Scooby went with the girls. One desultory conversation and several awkward silences later, Fred and Shaggy agree that from now on, they'll stick to the regular version.
In the series finale, Zuko and Katara head off to confront Azula, Aang goes to confront Firelord Ozai, and everyone else goes to stop the Fire Nation fleet.
In the previous season, Aang had gone off to learn from a guru, Sokka went to meet the Water Tribe warriors, Toph went to meet her mother and gets captured by the bounty hunters her parents sent to bring her home and Katara stays in Ba Sing Se to help plan and organise the invasion of the Fire Nation. Meaning none of them are around to realise that Azula, Mai and Ty Lee have infiltrated the city, until Katara discovered it too late.
The cartoon Johnny Bravo did a Scooby-Doo parody, which plays on the old joke that Freddy always said "Let's split up!" just so he and Daphne could make out while Scooby, Shaggy and Velma get chased by the monster-of-the-day.
Even Johnny of all people points out how stupid this is:
Johnny: "There's a monster out there and you want us to split up?" Freddy: "Well...yeah."
An episode of Captain Planet had the team looking for a firebreathing monster. Of course they split up. It takes Wheeler and Linka all of ten seconds to completely abandon the mission and move in for a kiss...which is when the monster shows up .
In another episode, Dr. Blight gave nukes to a couple of people in Israel, a couple in Northern Ireland, and a couple in South Africa...giving one to each side. The Planeteers had to split up to fight them.
Jonathon: All right, gang, we have to split up and look for clues. Stan: How should we split up? Jonathon: I know! Let's have everyone who enjoys having obstacles in their life which they can overcome go this way, and everyone whose insecurities sabotage their potential to overcome those obstacles go that way.
Made hilarious by the fact that everyone neatly separates into two groups without hesitation, and someone remarks "Well, that was easy!"
Kevin:Great idea. That way, Aggregor can pick us off one at a time.
In The Powerpuff Girls episode "Him Diddle Riddle," one of Him's riddles requires the girls to head for Chinatown and answer a ringing pay phone in a three-minute timeframe without flying. Blossom has the three split up and take the most convenient route to the phone with the first there to answer it. Blossom hitches a ride with an 18-wheeler, Bubbles takes a bus then a pony, and Buttercup takes the subway.
In the Space Stars episode "The Shadow People", Space Ghost and friends team up with the superheroine Elektra. While exploring a seemingly abandoned city, Space Ghost suggests they split up to cover more ground. Jace immediately asks to go with Elektra, but Space Ghost says Elektra is powerful enough to go on her own, much to Jace's disappointment.
In the Boy Scouts, they have something called the Buddy System, whereby you never go anywhere alone (climb a mountain, hike into the woods, go swimming in a lake, wandering off to use the latrine), because if you get injured or lost while you're alone, nobody knows where you are to help you, or to even know you need help. Similar practices in the Armed Forces refer to the buddies as "Wingmen", "Shipmates", or "Battle Buddies"
Some camps, such as the Philmont Scout Ranch, take this a step farther, and require that you travel in groups of four. So if someone gets injured, one can stay with him, leaving another pair to travel together to get help.
The whole "travel in groups of four while hiking" thing is taught in different cadet branches as pretty much standard logic. Because who'd want to be up a mountain by themselves?
It's not just the Boy Scouts. Not only should one never, ever scuba dive alone, but one of the quickest ways to never be allowed back on the dive boat is to surface with your buddy still below.
The trope is averted in schools that have young children. Children are typically never allowed to go anywhere by themselves except for the bathroom or if they have to give another teacher or faculty member something. Field trips make it more apparent since a child that goes missing can create a massive problem for the school, which is why some children are paired up with another child before the trip starts.
When a search for a person is underway by the police or a similar group, the search party tend to split up into smaller groups in order to cover more ground and increase the odds in finding the person they are looking for.
In the board game Betrayal at House on the Hill, even though you're all investigating a Haunted House, the only way to actually get anything done for the first half of the game is by splitting up. For the second half of the game... most of the time you want to get back together at quickly as possible.
Pointed out comically by Yahtzee when he reviews Space Marine FPS number eleventy billion. The dangers of being a voiceless marine become apparent when you can't respond to your companion's suggestions of splitting up by saying 'That's a fucking stupid idea!' Complete with a decapitated head animation.
In New Kids on the Rock episode 4, there is a lovely exchange on this subject.
Kevin: Let's split up. Ryan: I agree with Kevin. Kevin: Thank you, Ryan. (He wanders off) Ryan: Let's not split up. Kevin is filled with terrible ideas.
The tabletop RPG Dragon Strike comes with a video demonstrating a game. One player asks if she can split off from the party, and the dungeon master says "Of course! At your own risk." Later, everyone does end up splitting up. The MS Ting of the video at The Spoony Experiment comments "I told you not to split the party! This always happens!"
Another player gets the idea as well. But by the time he says it, everyone has spitted off.
Lampshaded in the Mansions Of Madness rulebook. In the section on player strategy, it advises against spreading out too much while noting how following this trope rarely ends well.