Cosmic Keystone

caption-width-right:320:[-In a realm beyond sight The sky shines gold, not blue There, the Triforce's might Makes mortal dreams come true.-] ""Who designed this campaign setting? Why would you include four points of such catastrophic weakness that tampering with any of them results in the destruction of the global ecosystem? It makes no sense! A kind and loving creator would never have done this, and a cruel one would simply have made the air out of acid. And it wouldn't have evolved on its own, as there's no advantage to living in a world poised on the brink of annihilation!""

- Red Mage, Eight Bit Theater, "A Deal with the Devil"

Oh no! The world is in danger! Happiness, sunshine, puppies and ice cream will cease to exist! Why, you ask? Well, it seems that the villains have stolen, corrupted, or destroyed the Four Orbs of Fate, the Pillars of Reality, the Tomes of Prophecy and Fate or The Lifestream. The loss of even one of these is enough to make the world spiral into a hellscape of torment that would make Satan weep molten tears of envy and pride. It seems that for some unfathomable reason the Powers That Be or Crystal Dragon Jesus who created the universe saw fit to make its continued healthy existence contingent on these poorly guarded, easily found, delicate, carry-on-luggage sized objects. Obviously they never heard of redundant systems and failsafes. These are also poorly designed, allowing less than scrupulous individuals to abuse them for personal gain.

Sometimes justified if the world/universe was once healthy and self sustaining but due to some catastrophe was broken requiring the hasty creation of a Cosmic Keystone by a benevolent precursor as a patch of sorts to hold the world together.

If the villain ever gets the cosmic keystone, expect him to try and use it to destroy and/or remake the world in his own twisted image to rule over. If he even realizes the reality-central nature of the item. Sometimes the villain has a smaller goal in mind for its power; he just doesn't believe it'll destroy everything if something goes wrong, or else has an overinflated opinion on his ability to prevent that from happening. If he doesn't have it he'll tail the hero, let him do the hard work of finding it, and snatch it from the heroes' grasp at just the last second, only to fly away cackling. One would think they'd know better than to tamper with the underpinnings of reality, but villains aren't the sanest lot. When the changes can be easily reversed, there is obviously No Ontological Inertia in that cosmos.

A person who is one of these is a Barrier Maiden, and possibly a Load-Bearing Boss. Settings where reality works via the Magical Underpinnings of Reality will probably have a lot of cosmic keystones.

Anime & Manga

 * In Digimon Adventure 02, the Digital World has seven Destiny Stones which maintain the barriers between realities. Each universe seems to have equivalents, our world's being Kyoto shrines. If all of any one universe's set of seven are destroyed, all dimensions will collide, destroying the multiverse. You'd think The Four Gods would have thought twice about leaving them all in plain sight and in the same city.
 * In X 1999, the world will essentially end if seven buildings in Tokyo are destroyed. Naturally, the Dragons of Earth tend to challenge the Dragons of Heaven to massive, destructive battles at these places.
 * In the Pokémon 2000 movie, three of the Legendary Birds maintained the balance of the world's climates. Capturing just one quickly threw the whole thing out of whack, turning a tropical area downright arctic. This is a massive change of theme from the Gotta Catch Them All mindset of the games; More like "Catch 'em all... except these three!" It's unknown whether this applies just to those specific three, or whether the capture of ANY Legendary Bird would have the same effect (or whether it would make a difference if the Bird went willingly).
 * When Ash meets one of the Frontier Brains, him and the others tell the Brain how impressive it is that he caught Articuno (although he didn't), showing that, at the very least, one CAN catch the birds as long as they aren't from the three islands. Either that, or Ash suffered from amnesia after that movie.
 * Considering the fact that later tournaments have competors packing Full Legendaries, it seems that the former is the case. Granted, however, the events in Pokémon Diamond and Pearl mentioned in the Video Game section below also occurred in the Anime ; making this a case of "depending on the Legendary."
 * One could make a very valid argument that except for the first, none of the movies obey the continuity of the show. The first movie had a lot of setup in the show, and is partially based on a plotline from the game, so it has to be canon. Plus it would get around the "how can Ash keep saving the world and yet nobody knows who he is" question.
 * One could make an argument, if it hadn't been Jossed by Word of God many, many times.
 * In Mahou Sensei Negima, the Magical World has literal Keys that can rewrite reality. The villains already have a few of these Keys, and used them to erase several Magical World inhabitants from existence . Obtaining the most powerful Key of them all is the main goal of the villains and the heroes (who want to undo the damage already inflicted by the villains).
 * The plot of Magic Knight Rayearth revolves around saving the kidnapped "Pillar of Cephiro", who supports the existence of the entire world with her prayers. The plot of Rayearth 2 revolves around
 * In Spider Riders the Oracle Keys where created to... Well I don't know exactly why they exist, except to tempt people into abuseing there power.
 * Transformers Cybertron revolved around the characters attempting to recover the Cyber Planet Keys and the Omega Lock. Optimus Prime needed them to save Cybertron, Starscream wanted to become a god, and Megatron wanted to destroy the universe and remake it in his image.

Comics

 * The Marvel Universe contains several objects capable of severely screwing up time and space, some of which bestow varying degrees of omnipotence on their wielders. These include the Infinity Gems (particularly when brought together and mounted in the Infinity Gauntlet), the M'Kraan Crystal, and the Ultimate Nullifier.
 * Most of the gods (and I mean Cosmic gods, not the local ones like Thor) are this as well, which is why they can't just kill Galactus or a Celestial. It's eventually shown exactly why killing Galactus would be a very bad thing, when somebody manages to actually do it: the Nigh Omnipotent Omnicidal Maniac Abraxas is unleashed. Galactus gets restored to life afterward.
 * In Bone, the Crown of Horns is the balancing point of both the physical world and the dreaming-world.
 * In the Lucifer comics God himself is the Cosmic Keystone, and his abdication leads to reality beginning to unravel (Though he had a plan to address this).
 * Nowadays in the DC Universe, the whole of the multiverse (fifty one universes to be exact) rest on top of the main Universe-0 (the fifty-second), more specifically on Earth due to all of the massive Crisis Crossovers. Should Earth-0 ever be destroyed, all of the multiverse would be destroyed (this was the goal of the Anti-Monitor in the Sinestro Corps War arc).
 * In the limited series "Trinity", the Big Three (Superman, Batman, and Wonder Woman) are cosmic keystones of the cosmic keystone earth.
 * As of Blackest Night the DC Universe got a new one: the Life Entity. As its name suggests, it is the source of all life in existence. In Brightest Day the Entity reveals to Boston Brand
 * In the Buffy the Vampire Slayer Season Eight comics, the Seed of the World, the source of all magic in this reality, is introduced.
 * The Incal.

Films

 * In Dogma, the cosmic keystone isn't an object, but a concept: God is Infallible. If God is ever proven wrong, existence would end. The movie's plot involves stopping two angels from doing that, by using Hollywood Catholic Dogma to end their banishment on earth.
 * The Fifth Element didn't just have cosmic keystones, but a living "perfect" human, the titular Fifth Element, was the focus and trigger for the only weapon that could fend off the elemental, perfect evil that wanted to destroy the world.
 * Slightly subverted in The Thief and the Cobbler, in which an Opening Monologue explains that the safety and balance of the Golden City depends on three golden balls perched on top of a minaret. News of an invading army comes just as King Nod discovers that the balls are gone, but the defeat of said army only seems to be incidental to the Thief finding and "returning" them.
 * The Golden Child is a living cosmic keystone, keeping the forces of evil from devouring the world through his Incorruptible Pure Pureness alone.
 * Smaller-scale version in Sgt Peppers Lonely Hearts Club Band with the original band's instruments, which protect the Sugar Bowl of Heartland USA. When they're stolen and scattered, the town decays into a sleazy shadow of its original self.

Literature

 * White gold in the Chronicles of Thomas Covenant is a cosmic keystone that is conveniently located outside of the cosmos it affects... until the start of the story anyway. The One Tree is another cosmic keystone, but with protections far surpassing the typical keystone. (Subverts the usual pattern further in that the Dark Lord never got his hands on them -- they were used by the good guys instead.)
 * Well, not really
 * The white gold itself isn't precisely a Cosmic Keystone; it's just a way to draw power from the real Cosmic Keystone, the Arch of Time. If the white gold is destroyed, nothing happens. If the Arch of Time is destroyed, reality (if you can call it that) will crumble.
 * The Dark Tower in the series of the same name. It manifests in all worlds, but only in one does it appear as an actual tower -- which is held up by six radiating Beams that span the sky in twelve directions from it. In most worlds, it takes the form of a rose, though it has also been known to appear as a tiger, a dog, or a talisman. One might question how a structure that is supposed to be the sustainer, or container, of all space-time can be threatened from inside the passage of time, but, you know, whatever.
 * Think endoskeleton.
 * According to Roland's palaver with the man in black at the end of the first book, there are infinite universes, and each one is a mere fundamental particle inside another, which is a mere fundamental particle inside another, ad infinitum. Each fundamental particle in each universe also contains another universe, and so on, forever and ever. Since each universe contains a physical manifestation of the Tower, that means that, as you expand beyond the billions of universes that your own is stacked inside (like Russian dolls), you're eventually going to discover that your own universe is a fundamental particle inside another universe's version of the Tower. Meaning that if the Tower gets destroyed, all of the infinite universes get destroyed too... because they're all, ultimately, within an infinite number of different versions of it. For example, Mid-World is inside a fundamental particle in the rose in Keystone Earth. The Tower is inside an infinite number of itself, it contains an infinite number of itself, each universe contains an infinite number of universes and is contained within an infinite number of other universes... everything is connected, and the destruction of one Cosmic Keystone is all it takes to bring everything down.
 * In an interesting twist, two entire universes function as Cosmic Keystones for The Multiverse. One the world in which the Tower exists as a real tower, and most of the characters' adventures take place. The other is (almost) our world, in which their adventures are described in a series of books by Stephen King -- actually referred to as the "Keystone World", and the only one for which time travel is impossible. Destroying the Tower in either of these universes would lead to all of God's (er, "Gan's") creation being unraveled.
 * One fascinating aspect of the Dark Tower series is its metafictional nature. The many fictional universes that were created by Stephen King are explicitly stated to revolve around the Tower, and it's directly implied that other fictional universes, including the Marvel Universe, the Star Wars universe, and the Harry Potter universe, are also connected to the Tower. The broader implication is that EVERY fictional universe is connected to King's creation, that the creator gods referred to in fictional works are ALL different aspects of Gan, the god of The Dark Tower, and that the Tower itself has a manifestation in EVERY fictional Verse. For example, by King's logic, the One-Above-All who appears in the Marvel comics would be an aspect of Gan, and the Triforce would be Zelda universe's manifestation of the Tower.
 * Susan Cooper's The Dark Is Rising series revolves around this.
 * The Boxes of Orden in the Sword of Truth series fit the trope, as using them incorrectly can let the Keeper, the local equivalent of Satan, into the world of the living. The Pillars of Creation are living versions.
 * The Holy Grail Lightstone is the Cosmic Keystone of the Ea Cycle. One would think something with that level of potential for abuse would have been guarded better.
 * The Young Wizards series has The Book of Night with Moon, a book which describes the entirety of existence and which must be read from periodically by wizards in order to remind Reality what it's supposed to be like. It's indestructible and can't be used by the Big Bad, but simply keeping it out of the hands of the good guys for long enough will result in reality slowly unraveling.
 * Played sort of straight in Robert Jordan's The Wheel of Time series with the 'invincible' cuendillar seals containing The Dark One being the key to his release and the apocalypse that would ensue as he rewrote the Pattern in his image.
 * Interestingly, Jordan plays with this trope as the seals are gradually weakening (and outright breaking in some cases) without any outside influence. This is generally put down to The Dark One breaking free of his prison, because the seals are the focus of the magic that's doing the actual imprisoning, so although they're invincible normally, as the magic gets damaged so do they.
 * Ray Feist's The Riftwar Cycle, and most particularly A Darkness at Sethanon, has the Lifestone, which draws power from and could be used to end all life on the planet. Justified as the creators thereof didn't give a good goddamn if they sterilized the planet so long as they won their war.
 * The Orb of Aldur and the Sardion in the Belgariad and the Malloreon are stones which embody the conflicting destinies of the universe and bestow godlike power on anyone they allow to hold them.
 * The Ruby Sunstone was said to be something like this for Dintopia in 'First Flight'; it would maintain a balance as long as it stayed in its place at Highnest, but trouble would ensure if it was removed. However, it may have simply been a legend or First Flight may not completely fit into the other books' canon, as the Sunstone was lost, then stolen briefly by Lee Crabb, then dropped into the sea during the final battle where Arthur and Will, helped by the Skybax,Northies and Giganotosaurs, managed to stop him.
 * The TV miniseries came up with a storyline about a ring of sunstones that kept the large carnivores in the basin, when some of them went out, chaos ensued.

Religion and Mythology

 * One interpretation of the biblical story of Adam and Eve holds that the Forbidden Fruit of the tree of knowledge essentially acted as a Cosmic Keystone. The serpent, who is supposed to represent Satan, tricks them into partaking of the forbidden fruit. The result, of course, is the fall of man and the ruin of God's perfect creation. Some believe that this is the reason why we have natural disasters, diseases, wars, famine, and death in the world today.
 * Interestingly, Revelation 5-6 and 8:1 speak of a scroll that is believed by scholars to be the title deed to the Earth. Now to whom could it belong?
 * In Greek Mythology, anyone who burns the entrails of the Ophiotaurus would gain the power to defeat the gods.

Live Action TV

 * The 1978-1979 series of Doctor Who revolved around the Doctor's needing to gather and assemble the pieces of "The Key to Time", scattered across space and time, before an evil power could get its hands on it. The villain had a particularly clever plot, too;
 * Altogether an inversion, The Key To Time is used to restore the universe's balance, which apparently gets upset all the time.
 * The new series also features an equation that can "solve" the universe, and somehow rewrite it to suit the solver's needs. The Doctor has to decide whether or not to use it to bring back the Time Lords and stop the Time War from happening. He didn't.
 * 'Logopolis', the final Tom Baker episode, features the titular planet which was itself a universal keystone. The people were bringing energy into the universe as a way to fight off entropy. When the Master decides to stop activity there for a little while (admittedly, not really understanding what they were doing) large chunks of reality were destroyed before the problem could be fixed. Even then, there was no reset button.
 * Power Rangers Operation Overdrive has the five jewels of the Crown of the Gods, each of which has a complicated series of MacGuffins as clues to its whereabouts.
 * In Season 5 of Buffy, we get "The Key" (note the capital K), a device which can destroy the barrier between realities and turn southern California into Hell on Earth.
 * ...How would anyone know the difference?
 * One would be a burning hellish landscape where ice and fire reign and the people are eternally tormented, while the other is hell.
 * Done in a slightly harder SF context in SeaQuest DSV. A deforested future Earth depends on ten massive air processing plants to keep what's left of the planet livable. Then a race of genetically engineered Super Soldiers - with lower oxygen requirements - decide they wouldn't mind the place to themselves...
 * The Emerald of the Eclipse in Tin Man.
 * in Lost.

Tabletop Games

 * In many fantasy RPGs is a common plot device used by Game Masters. Have the heroes find the Cosmic Keystone before the Big Bad can get to it and destroy it. Very much a form of stock plot.
 * Used very literally in the Dungeons & Dragons adventure module The Apocalypse Stone. The Stone of Corbinet (which must always be italicised) is the Cosmic Keystone used by the gods to create whichever world you choose to set the campaign in, and which connects it to the other planes. As long as it stays in Castle Pescheour, the Axis Mundi, everything's fine. The castle is watched over and kept secret by the Pescheour family and their servants. The Big Bad is an exiled prince of the family whose brother was chosen to rule the castle in his stead, and who doesn't even know what the Stone really does, but wants to steal it so he can play king himself. He sets the player characters up in an elaborate Batman/XanatosGambit to have them steal it in his stead with no idea what they're actually doing. As the world starts to fall apart gradually as a result and the heroes eventually find out what they've done, they must hurry to undo their mistake -- the Big Bad certainly isn't going to that, being evil enough to let the world be reduced to nothing if he can't have his way with things.
 * Exalted has a few examples, most notably the Elemental Poles and the Loom of Fate. Differ from most in that the Poles are incredibly durable and malleable (the four that exist at the edge of the world can adjust themselves to how far the edge happens to be), and the Loom is probably the best defended thing in the world.

Video Games

 * The Pillars of Nosgoth in Blood Omen: Legacy of Kain, though there it's subverted because the Anti-Hero protagonist decides to destroy the pillars completely and rule as an evil vampire king.
 * The Pillars are technically more of a representation of the state of Nosgoth as a whole, and they are maintained by their nine guardians, whose states of mind the pillars reflect. Alternatively, the player can choose to save the pillars by killing himself (him being, unknowlingly, the last pillar guardian), but canon says that he chose not to, condemning the pillars to eternal ruination.
 * Later games reveal that
 * The Final Fantasy series has many of these.
 * The original has the Four Orbs, one for each classical element. Their loss is what's slowly destroying the world. They were only called "Orbs" because "Crystals" wouldn't fit in the space allotted.
 * Final Fantasy III (the real one) had four elemental crystals, fairly standard stuff. Much like the elemental crystals of Final Fantasy V (see below), they give the heroes jobs. Unusually, they are neither destroyed, stolen, nor tampered with. They are losing their light, though, which is why the Wind Crystal summons the Onion Kids (or Luneth in the remake.)
 * Final Fantasy IV had not just four crystals for the elements, but an additional four dark equivalents for the underworld. While these crystals are never threatened within the time-frame of the game (merely used as tools to reach villains' goals), it is strongly implied that they are just as vital to the world as similar crystals other installments in the series.
 * And there's a second full set of eight on the Moon. Using both sets together is what enabled the Big Bad to send the Giant of Bab-il down to the world in order to raze it.
 * Final Fantasy V also had four crystals for the elements, the destruction of each in turn wreaking havoc with the given element.
 * Final Fantasy VI had the statues of the three goddesses, which merely moving out of alignment would cause the entire world to fall to pieces. Although they have that effect because they want to destroy the world, or at least don't care if it gets wrecked while they fight amongst themselves.
 * According to the Esper legend, the Warring Triad came to realize the horror they had brought upon the world, and voluntarily sealed themselves away. However, the raw magic that emanates from them is so powerful, they need to be sealed in a precise alignment to nullify each other, and prevent their mere existence from causing further damage.
 * Final Fantasy Mystic Quest had four Crystals very similar to the Orbs in the first Final Fantasy. Additionally, there was a Crystal of Light, but its significance to the world was never well-established.
 * In something of a reversal, Final Fantasy Tactics Advance had the protagonist going around destroying Ivalice's Cosmic Keystone set to turn the world back to normal..
 * In Final Fantasy IX, the Crystal is indeed a very Cosmic Keystone, as all life, everywhere, comes from and is sustained by it.
 * It's very much like that as well in Final Fantasy XI, as the Mothercrystal is the basis for all of Vana'diel. It was also absurdly hard to get to, originally, but when the thing trying to destroy it is a Cosmic Horror, that kinda doesn't matter.
 * In Final Fantasy XIII,  is the keystone that holds Cocoon together. Without it, all of Cocoon's Fal'Cie would die and Cocoon along with them.
 * The Legend of Zelda series features the Triforce which, while it cannot have such a powerful effect upon the normal world, will turn The Golden Land in which it usually resides into a reflection of the bearer's whim. The Triforce has canonically only been used directly a handful of times to grant wishes (Zelda II the Adventure of Link, The Legend of Zelda the Wind Waker, The Legend of Zelda a Link To T He Past, The Legend of Zelda Skyward Sword), and during the timeskip of The Legend of Zelda Ocarina of Time, Big Bad Ganondorf uses it to warp the Golden Land into Mordor.
 * In Ocarina of Time, Ganondorf makes a grab for the Triforce (whole) and it shatters: Power is given to Ganondorf, Wisdom goes to Zelda, and Courage goes to Link. The real Ganondorf has been with Power in almost every other game (A Link to the Past is a notable exception since the Triforce is actually all in one place for once), while Link is often on quests to retrieve Courage and Zelda almost always has Wisdom innately (with the original game being exception for both).
 * Which in turn explains his incessant desire to kill or otherwise "deal with" Link and Zelda, since the death of either will release their part of the Triforce, making it up for grabs -- exactly what Ganondorf wants.
 * The Legend of Zelda Twilight Princess changes up the mythos a bit: the Triforce is notably backgrounded, and new Light Spirits are added; without the Light Spirits, the Twilight Realm takes over the world. And the Twilight Realm has its own -- small suns that return Dark creatures to their original, more peaceful forms.
 * Tales of Symphonia has the Mana Tree, which in a subversion, has already been destroyed for the past thousand years or so. The entire point of the game is to create a new one.
 * Romancing SaGa pulls something more out of this, The legendary Artifacts; Fatestones, if not collected will be used to power up the Final Boss, you can even power him up intentionally for a greater challenge if you wish after clearing the game one time.
 * In Star Fox Adventures, General Scales manages to snag the four SpellStones that keep the planet together. Its initial effect is to push four chunks of land away from the planet, but there are concerns that the planet could explode. You don't need to worry about that happening, however; you can Take Your Time.
 * In Valkyrie Profile: Silmeria, the four worlds of the setting are each stabilized by one of the four treasures. Removing a treasure from its world causes that world to quickly become unstable and eventually cease existing.
 * The world of Wizardry VI, VII & VIII are chucked full of these. First theres the Cosmic Forge, a pen and book in which anything written (or erased) affects reality accordingly.
 * The four seals in Drakengard fill this role. Partially subverted in that.
 * In Zork: Grand Inquisitor, the world will stay a world oppressed by the technological dictator The Grand Inqisitor if the player doesn't find three object with massive magical power: a Cube of Foundation, the Skull of Yoruk, and the Coconut of Quendor.
 * In Nox, the player must find the Halberd of Horrendous, the Heart of Nox, the Weirdling, and finally The Orb.
 * In Diablo II, the evil Baal tries to capture the Worldstone. He aims to corrupt it and turn the mortal world into a bastion of Hell.
 * Golden Sun features the Elemental Stars, which when removed from their hidden chamber cause a calamitous volcanic eruption. Placing these stars in their respective elemental lighthouses will destroy the world.
 * The Elder Scrolls IV: Oblivion: Inverted in that the player goes around entering small hellish dimensions stealing their cosmic keystones in order to collapse them and prevent the demons within from attacking your world. Of course, the reason the demons are able to do open up the portals is because the Cosmic Keystone on your side (The Amulet of Kings) was stolen, and you need to get it back.
 * The Elder Scrolls III: Morrowind features the heart of Lorkhan, who is also the creator of Mundus and Nirn, in which the TES series takes place. Additionally, after having powered the massive golem Numidium once, the golem breaks reality each time it is turned on.
 * What's more, the events of Oblivion were set in motion by the destruction of the towers/stones - disguised cosmic keystones across Nirn, including the Heart of Lorkhan. With enough of them gone, Mundus is in trouble; this also suggests that Azura's motivations in steering the hero towards destroying the heart in Morrowind may have been out of different motivations than she let on. For such a surprisingly pivotal plot point, this is buried fairly deep in the lore, as they decided that "THE EMPEROR IS DEAD!!! DEMONS ARE COMING" was cooler and less confusing.
 * Oblivion revolves around three cosmic keystones: the Emperor's bloodline, the Amulet of Kings, and the Dragonfires. The Dragonfires maintain the barrier that separates Mundus from the  Daedric Realms as long as they remain lit. They were created through a bloodpact between the Emperor's ancestor and the leader of the Aedra, the dragon god Akatosh. Due to this, the fires only remain lit so long as the current Emperor is still alive; if the Emperor dies, another of the bloodline must relight the fires using the Amulet of Kings (which holds Akatosh's own blood) or else the barrier weakens and eventually vanishes. By the end of the main campaign.
 * Averted/Inverted in Suikoden, with it's 27 True Runes. The runes are major parts of the world, and at least one is required for the continued existence of it's domain (The Dragon Rune allows dragons to exist) and the destruction of the 5 True Elemental Runes is Not A Good Thing. In fact, it's implied (and the Big Bad of Suikoden III's plan is predicated on this premise) that the destruction of any one of the True Runes would destroy the world. However, the Runes are rarely in danger as they have wills of their own and generally control their bearer FAR more than their bearers control them.
 * Pokémon Ruby and Sapphire/Emerald were centered around this. Evil bad guy(s) steal(s) object(s) of power, world goes to hell.
 * Video Game Pokemon Diamond And Pearl/Platinum were even more centered around the trope, if that's even possible. There were even separate levels of Cosmic Keystones here:
 * To be fair, it WAS incredibly difficult. Cyrus DID have to . I would say that those are some DAMN well guarded Cosmic Key Stones.
 * Another D/P example is found in the postgame, when
 * The Time Gears from Pokemon Mystery Dungeon: Explorers of Time/Darkness/Sky. Not only are the Gears needed to stop the Bad Future, they are also needed in order to take the "Primal" out of Primal Dialga, the game's   final boss.
 * The first Ty the Tasmanian Tiger has five talismans that need to be recovered so the Big Bad of the series can't unlock the power of the Dreamtime and wipe out all the mammals. Incidentally, the place the talismans are returned to serves as the conveniently-located hub of the game.
 * Wild Arms has the Tear Drop - a crystal with a link to the guardians and should not be in the wrong hands. There's also the Ray Line, a sort of underground conduit linking the guardians' powers. When the villains manage to damage it, the forces of nature go out of whack, wreaking havoc.
 * And this makes more sense if you take into consideration Blind Idiot Translation: Ray Line = Ley Line. Indeed, it was translated as Leyline in the remake.
 * In Mother 3, the
 * In Vagrant Story, the city you fight in is the Cosmic Keystone. Yes, drawing on its power irrevocably damns your soul, and sometimes you can't even stop yourself from using it. Yes, it also unravels that pesky Laser-Guided Amnesia (OR DOES IT?). And yes, everyone and their grandmother has designs on the bloody place, including that Corrupt Church. All to the point where you don't know who might have the right idea up. Until the end, where it becomes a case of who's the last man standing.
 * Said Cosmic Keystone, named 'The Gran Grimoire', is the source of all magical energy in the world. And, in the Final Fantasy games that tie in with Vagrant Story, normally manifests as a book that created, and is holding together, the entire world.
 * The Infocom Interactive Fiction game Spellbreaker has its protagonist traveling the world in search of its Cosmic Keystones, which in a borderline subversion manifest as featureless white cubes that are utterly indistinguishable from one another (but can be written on to differentiate them; this was considered a neat feature when the game first came out).
 * Xenogears and Xenosaga both have the Zohar Modifier, an object that has existed since the beginning of the universe.
 * Chrono Trigger and Chrono Cross have a few of these -- the Time Egg (the "Chrono Trigger"), the Frozen Flame and the Chrono Cross. In the Fan Game Crimson Echoes, the Frozen Flame is the prominent Cosmic Keystone, while the Time Eggs have become more easily manufactured and used (with both Balthasar and Lucca constructing them), suffering Keystone Decay by virtue of this.
 * The Seven Seals in Darksiders are essentially a countdown to Armageddon. Breaking the Seventh is the signal for everybody to engage in the massive cosmic winner-take-all power struggle that is the Endwar, with the Horsemen ready to clean up the mess when everything is resolved.
 * Valerian Scarlet's Arc in Champions Online has you collect a collection of artifacts that have the potential to jump start the apocalypse. You know, so she can seal them?
 * The Stone-Like in Radiant Silvergun and Ikaruga.
 * Demons Souls has the Monumentals and the Archstones in the Nexus. The Monumentals, willingly transformed into half-living magical statues, sealed away the Old One the last time it went on a soul-devouring world tour, and created the six Archstones to bind together the remaining fragments of reality. If the Monumentals completely die out, or the Archstones get destroyed, cue The End of the World as We Know It.
 * The Flame of Olympus in God of War.
 * Nie R has
 * Dark Souls has the Lord Souls, fragments of the First Flame. These flames created disparity in a once ordered and gray universe, and the Lords wielded the power of these Souls against the everlasting dragons. The dragons were defeated, and thus began the Age of Fire, the age of Lords. The premise of the game is that the First Flame is flickering, and the world is slowly dying as a result. The mission given to your character is to rekindle the First Flame to save the Age of Fire.
 * In Turok 2: Seeds of Evil, the destruction of the five Energy Totems will release Primagen from his prison and destroy our universe.

Web Comics

 * Red Mage of Eight Bit Theater (a sprite comic based on Final Fantasy I) points out the ridiculous nature of this trope in the page quote.
 * The five Gates in Order of the Stick are somewhat more reasonably founded than most examples: they were placed over flaws in space-time in order to keep the Snarl, the local Sealed Evil in a Can canned. And the gods could indeed fix it, in the same way you can fix a horribly screwed-up computer by formatting and reinstalling... (which is to say, by starting over with a fresh world). The gods would do that if the Snarl is ever freed, so the protagonists are working to prevent it from being freed in the first place, for obvious reasons.
 * In Emergency Exit the main cast was assigned to collect "artifacts" in order to save someone's world from destruction, but it turns out to be a flat out lie and now nobody seems to know what they are for. It is shown that each artifact has a minor power, but implied that they do something far more spectacular when put together (hence an alternative collective name for them, "The Puzzle").
 * In City of Reality, the Aura Stones appear to be this for the various Alternate Universes. Each world has a master stone which allows its particular "reality" to exist, and removing or destroying this stone may have catastrophic consequences.
 * Cucumber Quest has the Disaster Stones, which, if all gathered, can be used to resurrect the Nightmare Knight.

Western Animation

 * Pirates of Dark Water had thirteen treasures which kept the evil, omnivorous Dark Water from escaping. The show's central premise is recovering them before it's unsealable.
 * Thundercats had scads of these. Most of the second season was taken up recovering the sacred treasures of Thundera in order to restore and stabilize said planet after it was originally destroyed.
 * Magi Nation has the eleven Dream Stones.  If they are brought together, they form the Core Glyph, which can seal Agram away for good. However, if Agram and the Shadow Magi get them, Agram can break free of the Core.
 * In the X-Men animated series, people with Psychic Powers proved to be Cosmic Keystones when brought together, as killing them all at once would have allowed to remake the universe in his image.
 * Albeit only if it was done in the Axis of Time, a kind of convergence of history existing outside of time. Plus, being in the Axis increases the psychics' powers, such that all of them gathered together collectively overpowered Apocalypse. So somewhat more stable than most Cosmic Keystones.
 * In Code Lyoko, entering "Code XANA" into a Way Tower will destroy the sector it is in. Furthermore, Lyoko can be deleted all at once by destroying the "Core of Lyoko" in Sector 5.
 * In Avatar: The Last Airbender, the spirits of the moon and ocean, bored with existence in the spirit world, came to live in the mortal world in the form of koi fish. If they are killed, the part of nature they represent (or the effect it has on other objects or something) will be gone forever.
 * Although one of them was smart enough to
 * In essence, the spirits took mortal form as a way of maintaining the balance of the cycles of the world. The destruction of one puts the other out of balance, in a manner which would destroy the world's cycles disastrously.
 * The Avatar Spirit, the source of the Avatar's power, is the spirit of the world itself. If the Avatar dies while in the Avatar State, the Avatar Spirit dies with them. Exactly what this would do to the rest of the world is never specified, but surely it would be a very bad thing.
 * One episode of Futurama featured a box containing the universe. Played for laughs, as even with warnings that it had to be treated as dearly as life itself, the box is shaken to listen for anything rattling inside (causing a small earthquake) and sat on (stretching out the picture horizontally).
 * The plot of Barbie and the Diamond Castle involves the heroines trying to keep the titular castle and the instruments in it out of the villain's hands, lest the world turn to "shadows and sorrow." The villain's actual goal in gaining the castle is to solidify her position as the only muse and rule all music, but those side effects will occur, apparently.
 * The Teenage Mutant Ninja Turtles Special Turtles Forever has  as a Cosmic Keystone for the entire Multiverse. Called "Turtles Prime", it is, basically,  . Destroy it, and the Turtles Multiverse will literally be erased from reality.