Planescape is a Dungeons & Dragons setting, centered around its very own City of Adventure: Sigil, the City of Doors.Much of the material that would become Planescape was initially introduced in the supplement Manual of the Planes in 1987 by Jeff Grubb. In 1989, the Spelljammer setting linked previous settings, including Dragonlance, Forgotten Realms, and Greyhawk, by allowing player characters to travel the Prime Material Plane, an infinite void in which each of the other settings exist as planets. Planescape, released in 1994, links Spelljammer with the Manual of the Planes by incorporating the Prime and other planes of existence into an even larger network of worlds and magic portals.In 1999, it became the setting for the Cult Classic video game Planescape: Torment.Sigil is a strange, Gothic, and often raucous metropolis that lies outside the rest of the Multiverse, inhabited by all manner of odd folk and ruled by the mysterious Lady of Pain and political parties—"philosophers with clubs", in more ways than one—called the Factions that Player Characters could join, all of them searching for the Truth behind the Multiverse. It is the hub of a vast network of magic portals that lead to many places, including:
The Inner Planes, each of which is based around a theme regarding matter and energy. For example, in the Plane of Fire, everything is on fire, on the Plane of Water everything is underwater, etc.
The Outer Planes, based on the alignments. Nine of the outer planes correspond precisely to an alignment; the other eight are in in-between spaces. For example, Mechanus (also known as Nirvana) is a Lawful Neutral clockwork universe which seems to consist mostly of gigantic gears tended by robot-like beings; while Baator, the Lawful Evil plane, is literally Hell, and Bytopia is a Lawful Good / Neutral Good plane founded on the idea of honest hard work. The Outer Planes are the literal afterlife where the gods live and their followers go when they die—it just turns out that with the right keys, you can walk there. This is an invoked, in-universe example of Character Alignment.
"Pathway universes", the key elements of the magic portal network, including the Astral Plane, the Ethereal Plane, the Infinite Staircase, and Sigil itself.
The factions, which form the backbone of character interactions (and fill the splat role), are:
The Athar or Defiers, cynical atheists and agnostics who believe the gods are frauds.
The Believers of the Source or Godsmen, who believe that life is a test and that any person can ascend to divinity.
The Bleak Cabal or Madmen, who believe that there is no meaning in anything.
The Doomguard or Sinkers, who believe that entropy must destroy everything so something better can rise from the ashes.
The Dustmen or the Dead, who believe that life and death are both illusions and seek oblivion.
The Fated or Takers, ruthless egotists who believe that right to ownership derives from the strength to take and hold it.
The Fraternity of Order or Guvners, who believe that power comes from the knowledge and exploitation of natural and societal laws.
The Free League or Indeps, individualists who paradoxically reject the faction system while being a faction unto themselves.
The Harmonium or Hardheads, authoritarians who seek to unite the planes in peace under one rule—theirs.
The Mercykillers or the Red Death, who believe mercy is weakness and true justice comes from violent retribution.
The Revolutionary League or Anarchists, zealots who believe all societal laws must be overthrown—but to what end, none can agree.
The Sign of One or Signers, who believe each individual creates the universe around them.
The Society of Sensation or Sensates, inveterate hedonists who seek enlightenment through new experiences.
The Transcendent Order or Ciphers, who believe that enlightenment comes from action from pure instinct, not thought.
The Xaositects or Chaosmen, who see truth in chaos and unpredictability and act accordingly.
Planescape is in many ways the thinking man's D&D setting. Players couldn't always fight their way out of a pinch, and the setting's philosophical theme and emphasis on the power of belief encouraged players to come up with inventive, cerebral ways to solve their problems. These themes were helped by the art and style, especially that of Tony DiTerlizzi, which emphasized gothic, neo-Victorian strangeness and Grunge rock influenced cynicism and attitude over the muscular heroes and glorious violence of other settings.The webcomics Planescape: Metamorphosis and Planescape Survival Guide take place in this setting, as does Shemeshka's Planescape Storyhour.
Planescape provides examples of:
Always Night: Lunia, the first layer of Mount Celestia, is an unusual positive example of this trope. The layer is an eternal starry night on the pristine beaches by a freshwater sea of holy water. Karasuthra, the third layer of the Beastlands, is another positive (though perhaps less calming) example.
The Anti-Nihilist: The Bleak Cabal, as described above. They have concluded there is no inherent purpose or meaning to the universe, and yet they see this as giving them no reason to contribute to suffering and every reason to contribute benevolence and kindness. As a result, they run not only the official Bedlam House of Sigil (which has far better conditions than any normal Bedlam House), they are also the faction most responsible for running orphanages and soup kitchens.
Arcadia: There's actually an outer plane called Arcadia. It's a realm of pastoral splendor dotted with orderly villages. Very orderly villages. As the plane of good-influenced lawful neutral, it's a place of peace and stability on one hand, and conformity on the other.
Banned in Sigil: The accessory The Factols' Manifesto was an amusing In-Universe example of the Trope. The Interactive Narrator of the book was its unnamed editor, who claimed that the book had been outlawed in Sigil and that he was a fugitive and one of its most hated citizen because he had turned whistleblower on all fifteen Factions and exposed their biggest secrets by writing the book. (He claimed, however, that the Lady herself confronted him once one dark night, and he assumed, as she let him live, that she did not object to his work. In Faction War, he was revealed to be background NPC A'kin, the Friendly Fiend.)
Bedlam House: The settled parts of Pandemonium are sometimes this trope. The entire Outer Plane consists of lightless tunnels blasted by a constant wind that quickly drives residents insane.
Averted by the Gatehouse, the asylum run by the Bleak Cabal, which is relatively safe.
Black Comedy: How many settings would publish a picture of a smiling devil parodying the famous Kitchener "I Want You" recruitment poster?
Cessation of Existence/The Nothing After Death: The Dustmen's belief is a weird mixture of this, reincarnation, cynicism, asceticism , and the "life is suffering" brand of nihilism that is more commonly used to fuel Put Them All Out of My Misery type villainy. The Dustmen believe existence as we know it is actually a massive array of hells known as "False Life", because living in it brings suffering and disappointment. All people in The Multiverse have already died and passed from the state of "True Life" (which they believe is a form of paradise) and are undergoing purgatory by suffering, "dying", being reincarnated into another stage of "False Life", and thus suffering again. The Dustmen thus practice a Buddhism-like form of asceticism, and try to encourage the others to do the same, in hopes of transcending their suffering and reaching a state they call "True Death", where there is no more suffering. Individual beliefs about what lies beyond True Death vary from this trope to being reincarnated back into "True Life" again.
Chaotic Stupid: Players of Xaositect characters were actively encouraged by the rulebooks to act this way (much to some other players' chagrin).
Clap Your Hands If You Believe: The central point of the setting. The collective weight of the factions' beliefs—the Sign of One in solipsism, the Fated (Takers) in social darwinism, the Harmonium in statism, and so on—can allow its most powerful members to alter the very physical and spiritual fabric of the Outer Planes.
Also the gods themselves. Gods gain power based on how strongly their followers believe in them. Gods with more followers tend to be stronger than gods with fewer followers, and they can give that power back to their followers in the form of spells for their clerics.
"Belief = Power" is a fundamental law of physics in the planes.
City Guards: The Harmonium keeps the peace with extreme prejudice, always ready to beat up those who cause trouble. The Mercykillers do a bit of this as well, and are even more violent.
Generally speaking the Harmonium keep order and arrest lawbreakers, the Fraternity of Order do the judging and determine sentence, and the Mercykillers handle imprisonment or execution (unless the victim is legally insane, in which case the Bleakers handle containment). If the criminal is violent/dangerous enough to warrant 'kill on sight' that's also the Mercykillers' business.
The City Narrows: Sigil's got one of these in the form of the Hive, a crime-ridden and mazelike slum. The Lower Ward, with its toxic air and numerous portals to the Lower Planes, might also qualify.
City of Adventure: Not only can you find practically anything in Sigil if you know where to look, it has portals that go to everywhere in the multiverse, literally. Sigil is not only an adventure onto itself, it leads to every adventure a creative DM can think of.
City of Weirdos: No matter how many strange entities you've seen while wandering Sigil, there are still stranger ones you've yet to meet.
Crapsack World: In many ways, Sigil, where the police force is run by a bunch of Knights Templar who believe that All Crimes Are Equal and everyone is guilty of something, while the taxes are collected by the faction that subscribes to a sort of weird mishmash of Randian Objectivism and outright thuggery. And then, of course, there are the actual planes that are Crapsack Worlds, like the seven different versions of Hell (which each come with at least three layers of variety).
Dark Is Not Evil: The Dustmen faction are basically all creepy goths who hang around with the undead, but their faction philosophy is akin to Buddhism and they're responsible for Sigil's funerals, proper treatment of the dead and counselling those left behind. The undead they hang out with volunteered to have their bodies reanimated, and are usually just simple laborers. Although it's true that in many ways the Dustmen's philosophy is actually bleaker than the Bleak Cabal's (the Bleakers believe there is no inherent purpose to life; the Dustmen believe life is suffering and one should use asceticism to pursue Cessation of Existence instead of the reincarnation that is "the norm").
Also the Doomguard, who believe in entropy and the inevitability of everything that exists eventually crmbling to dust with nothing remaining at the end of time. Some extremists believe that they should speed up the process as much as possible, while others support the constructions of new buildings, because it includes chipping away mountains and cutting hundreds of trees, and the new building will only last for a few hundred years if it doesn't burn down much earlier.
The Bleak Cabal are extreme nihilists, most of whom have at least a trace of mental illness. But despite that and their ominous moniker, they run Sigil's orphanage and soup kitchens, as well as asylums that at least try to not be Bedlam House. The reasoning ends up being genius: if there's no point to anything, there's no existential reason to not help each other, and if we live in a Crapsack World, there's no need to make things worse.
It should be noted that all three of these Factions have both good and evil members. Neither moral belief is a prerequisite for joining any of them. (And Player Characters are welcome to join any of these groups, should they desire, with no fear of moral repercussions.)
Demon Lords and Archdevils: Planescape brought them back to D&D for the first time since the game was "sanitized" in the switch to 2nd Edition. They had to call them "Tanar'ri Lords" and "Lords of the Nine", until the adventure Dead Gods, when Orcus was explicitly referred to as a demon.
Specific examples that played a significant role in adventures include the demon Orcus in Dead Gods and the devil Dispater in Fires of Dis.
In addition to the fiendish rulers, the Slaad Lords (Ygorl, Ssendam, Chourst, and Renbuu) and Primus of the modrons filled similar roles.
Endless Daytime: Krigala, the first layer of the Beastlands, is an eternal and glorious afternoon.
Enemy Civil War: The eternal, devastating Blood War between the baatezu (devils) and tanar'ri (demons) is the only thing keeping the lower planes from overrunning the multiverse.
Smaller-scale (but no less bloody) examples include the constant war between the tanar'ri lords Demogorgon, Orcus, and Graz'zt; and the feud between the gods of the orcs and goblins on Acheron.
The Eeyore: Not unusual for The Bleakers (charitable variant) and The Doomguard (destructive variant). Pretty much all Dustmen are like this, too, given that happiness is literally the enemy according to their philosophy.
Every Man Has His Price: Nowhere in the universe is the phrase "money talks" truer than it is in Sigil. You can use bribery to get nearly anything, information, entry into places you wouldn't otherwise be allowed, and maybe getting the town watch to look the other way. (The only folks in Sigil you can't bribe, usually, are the Guvners, Harmonium, and Mercykillers, but even then, a few evil members of those Factions will "compromise" in exchange for a "donation" or two.)
Evil Tower of Ominousness: Several. Khin-Oin, in the Gray Waste, is a tower in the shape of a spinal cord reaching forty miles into the sky and forty miles under the ground.
Existentialism: Probably the central theme of the setting. Worship of gods plays no major role in Sigil, instead the factions dominate society, trying to shape it according to their believes in the meaning of existance in the abscence of a "true" higher power that stands obove everything.
Fantastic Slurs: Several of these abound, the most outstanding being "prime" and "clueless."
A prime is someone from the prime material plane (i.e. an actual Earth-like world, such as most regular settings) rather than from Sigil or the outer/inner planes; to some people, this implied that the person was rural, uneducated, the "country cousin from out of town," although technically it's purely descriptive and not derogatory.
A clueless is Exactly What It Says on the Tin; someone who just doesn't get how things work out among the planes, and sometimes believes he's still back home — an apt comparison would be your country cousin visiting the city for the first time, and your retarded cousin who can't be convinced he has to wear pants when he's with other people. Some people consider all primes to be clueless, but there's a good deal of arrogant cluelessness among some planewalkers, too...
Fantasy Counter Part Culture: Of dozens of cultures, or rather how those cultures' myths would play out. For example Olympians and Chinese deities coexist with Egyptian, Finnish, Japanese, and Native American mythology without too much clash.
Fate Worse than Death: Pissing off the Lady of Pain can have any number of messy, painful results, but her most famous punishment is Mazing; sending the offender(s) to a pocket dimension labyrinth of her own making. These mazes can be of any make or structure, and the Mazee is immortal, unable to age or die from injuries (self-inflicted or otherwise) or starvation/thirst, possibly leaving them to run the maze for the rest of eternity. The only way out is to finish the maze. However, even if they escape, it's possible for the offender to exit into a completely different place or time, sometimes thousands of year in the past or future. Only way to avoid this fate: DO NOT PISS OFF THE LADY OF PAIN.
Fictional Counterpart: A strange version, where Baator is clearly based on Dante's Inferno, Mount Celestia on his Purgatorio, and many locations or characters are adaptations of real-world myths, such as Olympus, Yggdrasil, and the Styx. Likewise, the factions are mostly fictional counterparts and send-ups of real-world beliefs, from the Randian Fated to the solipsistic Sign of One.
Fire and Brimstone Hell: Plenty of these. Phlegethos, the fourth layer of Baator, is probably the most traditional. The Abyss, being what it is, is sure to have several layers that meet the criteria. The top two layers of Gehenna also fit, though they're a bit less traditional about it.
Flaying Alive: Just one of the many consequences of pissing off The Lady of Pain.
Garden of Evil: Cathrys, the second layer of Carceri, is called the Crimson Jungle. It's a tropical hell where the trees drip poison and razor-edged grass can disembowel the careless (or even careful) traveler.
Ghibli Hills: Dothion, the bottom layer of Bytopia falls into this category. It's a pastoral land where the natives live in small and industrious villages, embracing the virtues of craftsmanship and honesty. Parts of Elysium may also qualify.
A God I Am Not: The Lady Of Pain. Her powers make her a deity for all intents and purposes, but for unknown reasons, worshiping her or referring to her as a goddess is one of the quickest ways to bring down her wrath.
The most common theory is that active worship could make her a goddess. The whole idea of Sigil as a neutral ground crossroads of the multiverse is that gods have no access there. If the Lady became one, the whole barrier would collapse in a Puff of Logic.
God of Good: Possibly Chronias, the top layer of Celestia. Never explicitly described, it is the final goal of the petitioners making the slow ascent up the holy mountain. There, they hope to be eternally joined to Celestia itself.
Good Is Not Nice: The Celestials can really ruin your day if you give them a reason to.
Global Currency: While this is an unofficial rule in almost all RPG settings, it's an official rule in this one, mentioned in the core rulebook. Gold from one world is considered just as valuable as it is from another in Sigil. (And Sigil is a place where the rule "Money talks" is truer than anywhere else.)
Gravity Is a Harsh Mistress: Certain planes, such as the Plane of Air, have "subjective directional gravity," which fits the "Gravitational Cognizance" version of this trope.
The Hedonist: subverted with The Sensates. The Sensates consider such beings a mockery of their belief, so characters like this do try to join, but if they just repeat the same pleasures over and over, they are invited to the Gilded Hall on Arborea—great palace of the eternal party on the Chaotic Good plane already biased toward overlong feasting. It's open, but since a hedonists have no reasons to leave the Happy Place incarnate, they spend the rest of their lives lost in indulgences and are buried on the premises (presumably with a great commemoration feast). True Sensates are Sense Freaks, devoted to experiencing every single sensation in existence; pleasant, horrid, and the whole gamut in-between. Or at least "specialize" in finding and discerning all the fine flavours of a some general type of experiences.
Hell: Baator, home of the baatezu (better known as "devils") is literally Hell, though all of the Lower Planes have elements of the trope.
Hell Is War: There are seven distinct Lower Planes, each of which is a Hell of sorts. Each of these has multiple dimensions. Of the seven lower planes, five are involved in the Blood War and one is given over to endless, genocidal wars between goblin-kind and orc-kind, with other races being thrown into the mix. So six of seven hells are invoke this trope.
Humanoid Abomination: The Lady of Pain. No one knows exactly WHAT she is, but she does not count herself amongst the gods, and they sure as hell don't want her amongst them. And she's powerful enough that the gods cannot step into Sigil. AT ALL. Not a single one. And within its walls, she is absolutely omnipotent. The laws of physics and magic are literally hers to command. If that doesn't scream eldritch abomination, what does?
In Which a Trope Is Described: Many of the game's books start with such an introduction, and their table of contents often have such a short sentence to describe every chapter.
It's Pronounced Tro-PAY: Some inhabitants of Sigil take serious offense if you pronounce its name "Sijil" rather than "Sighil".
Knight Templar: Most of the Mercykillers ("Justice at all costs") and a large portion of the Harmonium ("We know what's good for you").
Lawful Stupid, Chaotic Stupid: The Fraternity of Order and (especially) the Xaositects were often painted this way by players, respectively. Modrons and Slaadi are so steeped in Order and Chaos respectively that sometimes they are borderline Starfish Aliens.
Literary Agent Hypothesis: Almost ever accessory for the setting is like this, written under the premise that some scholar or researcher from Sigil is writing down the information from personal experience. Notable examples include the unnamed fugitive editor of The Factol's Manifesto, mentioned above, and Faces of Evil: The Fiends, supposedly edited by the tiefling Ice the Trice Born with the aid of a collection of oddball narrators (not all of them, Ice regrettably tells the readers, survived to see the book printed, but she won't say which ones). The most entertaining one in the book is, without a doubt, the blue slaad Xanxost.
Lord British Postulate: The Lady has no official stats in order to avert this trope, and also because it would take away her mystery.
Moral Dissonance: The Upper Planes allow the Blood War -— an eternal conflict that would be seen as bloodthirsty even in the Warhammer setting (if not its more-famous sci-fi cousin) -— to continue without end since it pits the two main fiendish factions against each other, and away from the good folk. The problem is, the Blood War seems to have a corrupting influence all on its own. This is explored more thoroughly in Planescape: Torment.
My Species Doth Protest Too Much: Fell is a 'fallen' Dabus, one of The Lady's servitors, who chose to abandon her service and worship the god Aoskar. The Lady responded by killing Aoskar and razing his temple in Sigil, but left Fell alive. People tend to be wary around him, believing him cursed.
Nay-Theist: The Athar. They do actually acknowledge a Higher Power — they simply believe that all of the gods and similarly-powerful entities in The Multiverse are simply not "really" gods and mere pretenders who mislead others to prevent them from reaching the Higher Power.
Necessarily Evil: The Lady of Pain is greatly feared for her ruthlessness, but most people acknowledge that, without her, Sigil would be nothing but a battlefield.
Nature Is Not Nice: The Beastlands is one of the Upper Planes, a place of untamed nature at its most glorious... and even good-aligned travelers should still watch their step. The Outlands, the neutral plane, has "nature red in tooth and claw" as its ethos.
No Pronunciation Guide: Just how does one pronounce baatezu, tanar'ri, or Xaositect anyways? A Player's Primer to the Outlands and Planescape: Torment helped a bit, but not enough to stop endless arguments at the game table.
TSR briefly did have a recorded pronunciation guide on their website. Sadly it was taken down with their abandonment of the Planescape setting. Not that this had any effect except to intensify arguments over whether they were "right."
The real reason was that TSR was afraid that Moral Guardians would accuse D&D of being Satanic (more than usual) if demons and devils appeared in the game. A Planescape adventure (Dead Gods) was actually the first TSR product that reverted to the use of "demon" over "tanar'ri" after the Satanic Panic died down.
The Old Gods: Naturally, there are things more ancient and powerful than the familiar gods out there on the endless planes.
One such being is one of "true Baatorians" who occupied the hells before devils came along, manifesting as an invisible, intangible force that siphons life and energy. It's explicitly meant to be one of those things that can't be challenged or explained, and apparently the present-day Baatezu would be very happy if it stayed asleep.
The Lady of Pain herself was long suspected of being one, thanks to her power to keep gods out of Sigil. It's pretty much confirmed at the close of Die Vecna, Die! the final adventure of 2nd edition D&D, when she literally changes the rules of the game and ushers in 3rd edition.
Orcus on His Throne: Not the trope-namer (as that would be AD&D's 3rd edition), but Orcus is around, and presumably has a throne in the Abyss on which he can sit. Another example might actually be Asmodeus, though he's pretty active in terms of scheming.
The adventure Dead Gods reveals what Orcus has been up to, and he is certainly not sitting on his throne. He's dead, but that doesn't stop him from almost destroying the multiverse.
Order Versus Chaos: Arguably more important than good versus evil. The Blood War between the chaotic tanar'ri and the orderly baatezu is perhaps the most famous example.
The Plan: Most factions run one. Except for the Xaositects, who think The Multiverse is one big Gambit Roulettemess-up run by no one in particular and behave accordingly, the Ciphers, who live by Don't Think. Feel, the Bleakers, who think that there's no inherent point to existence, and the Indeps, who just want to be left alone.
Polluted Wasteland: Found in several of the Lower Planes, but special mention should go to Maladomini, the seventh layer of Baator. The ruling Baatezu, Baalzebul, is obsessed with building the perfect city, but is never able to create something that meets his satisfaction. The layer has been completely laid to waste in his quest to find more building materials. Cities of impossible beauty dot the blasted layer, abandoned because of some petty flaw that only Baalzebul can see.
Portal Door: These are all over the place, but mostly in Sigil, so much that it's sometimes called The City of Doors. You can find a portal there that leads anywhere, literally, if you know where to look.
Ragtag Bunch of Misfits: The Free League is a gathering point for people who don't believe too strongly in any faction philosophy one way or the other, banding together for common protection. They include many of the city's merchants and innkeepers, who benefit from being neutral.
Red Sky, Take Warning: Several parts of the Lower Planes, including Avernus in Baator, Pazunia in the Abyss, and several layers in Carceri.
Romanticism Versus Enlightenment: Most of the Lawful factions and races are Team Enlightenment, most of the Chaotic factions and races are Team Romantic, and everyone else does have a stake in the conflict. The Blood War is a war to decide whether Evil is Romantic or Enlightened. As expected, no one is deemed right.
Scavenger World: Most of the Lower Planes have aspects of this, though special mention should go to Thuldanin, the second layer of Acheron. Powerful weapons have a way of finding their way to this war-torn layer, and a lucky artifact-seeker can really hit it big.
The Scottish Trope: People of Sigil believe that referring to the Lady of Pain by her full name makes her pay attention, and thus refer to her as 'The Lady' if they must mention her at all. They prefer to talk around mentioning her at all if they can.
Series Mascot: The Lady of Pain, given the fact that her face is on the logo, making her ominous glare grace every product.
The Modrons are the inhabitants of Mechanus, and resemble clockwork geometric shapes possessing some combination of limbs, tentacles, and facial features. Divided into different ranks (the most well-known being the cube-shaped quadrones), the Modrons are the living embodiments of law and order. A Modron of any given station is only aware of the ranks immediately above and below it; anything beyond that simply does not register.
Sometimes Modrons are touched by chaos and go rogue. This doesn't mean that they start wantonly breaking laws and living large; they're still lawful to an alien degree, just slightly less so than their peers.
The frog-like Slaadi are to chaos what the modrons are to order.
Stop Worshipping Me: The Lady of Pain. Seriously, stop worshipping her unless you want to meet a horrible fate. She has a... complex about it.
Straw Nihilist: The Dustmen, arguably, as one could argue that their philosophy (all existence is a hell meant to make us suffer, and dying merely causes us to be reincarnated here to suffer again, so we must seek to deny everything that is pleasurable in life so that we may pass into true oblivion and utterly cease to exist) is, in many ways, bleaker than that of the Bleak Cabal.
Tailor-Made Prison: The Mazes, pocket dimensions that the Lady of Pain creates out of Sigil as prisons for anyone who threatens the city. These small dimensions are just that complex maze-like prisons. They aren't completely escape-proof, as the Lady always includes a well-hidden way out, but it's rare for anyone to escape. (Some people think that she includes the escape route to torment the prisoner.) (Note that for someone who does something that warrants the Lady's attention, this is a lenient punishment. If someone really makes her angry, then magic is needed to identify his remains.)
Thirsty Desert: Minethys, the third layer of Carceri. A crimson and demon-haunted desert.
Through the Eyes of Madness: Factol Lahr of the Bleak Cabal discusses this in the Factol's Manifesto. The entire Bleak Cabal faction qualifies. Faces of Evil discusses the demons via the cheerful, hilarious eyes of a mad slaad. And insane characters show up with surprising frequency.
Toad Licking: One of the flavor text quotes a Sensate's opinion on licking a Slaadi. He says that it is a horrible mistake... that everyone should make once in their life.
Truce Zone: Sigil, in both the official materials and the fan expansion site <mimir.net>.
The Voiceless: The Lady of Pain. There is only one confirmed case in Sigil's history where she has been known to utter a sound, and that was at the end of the module Die, Vecna, Die!. (Factol Nilesia once made a claim that the Lady spoke to her in a dream, but Nilesia's sanity was questionable at best.) In the rare times that the Lady needed to communicate with someone, her entourage of dabus spoke for her.
War Is Hell: Acheron. Just as Ysgard is Warrior Heaven, Acheron is Soldier Hell, where souls of ruthless professionals, conscripts drunk on the bloodshed, all those who lost sense of what they fought for, fight as cannon fodder in pointless never-ending wars.
Warrior Heaven: Ysgard! The happy souls who call this plane home live it up Viking-style, fighting each other in grand melees all day. Death for residents is temporary, and when the sun sets they retire to a drinking hall to boast about their deeds. The rule about coming back to life doesn't apply to visitors, however.
The fifth layer of Mount Celestia is the Holy Warrior Heaven. Everyone regenerates, including visitors, and it could best be summed up as what would happen if infinite paladins got together to make a stronghold. It is strongly implied all paladins are allowed at least this high on the Mount.
Well-Intentioned Extremist: The factions in general are like this, at least a lot of the most influential members of them are, some more than others. Their goals are all different, and most conflict with each other, but many members take their philosophies to extremes, sometimes dangerous extremes. (The Guvners are a bunch of Rules Lawyers who want to take over the universe using laws and the Xaositects don't like laws at all, and want to see ALL of them abolished. Neither idea would be good for the universe in general.)