''Mystara'', also known as the ''Known World'', is the default setting for the Frank Mentzer version of Classic ''TabletopGame/DungeonsAndDragons'' (the Basic, Expert, Companion, Master, and Immortal sets; and the Rules Cyclopedia by Creator/AaronAllston, which compiled the rules from the first four sets into one volume).

This setting comprises both the "Known World", the regular world that adventurers start out in; and the "Hollow World", a mysterious, gigantic subterranean world that the characters can explore later on in their careers. Probably the biggest difference between this setting and other ''D&D'' settings (apart from its cosmology) is where the clerics of the setting get their spells. Clerics serve one of the Immortals, mysterious and powerful beings that serve the five Spheres of Power, hoping to either expand the influence of one of the spheres or maintain the balance between them. When Immortals meddle in mortal affairs, it is indirectly, and often through some kind of avatar. As characters in the setting reach the pinnacle of power, they have the chance to become Immortals themselves.

Mystara was the setting that most people of the 1980s who got into ''TabletopGame/DungeonsAndDragons'' were familiar with, with such familiar faces as Morgan Ironwolf the fighter, Sister Rebecca the cleric, Silverleaf the elf, Frederik the dwarf, Black Dougal the thief, Creator/LarryElmore's beautiful cleric Aleena, and Bargle the Infamous, the bastard of a magic user who murdered her and who every player of that day wanted to take down.

The ''Red Steel'' sub-setting has personal magical powers and deforming curses. The [[http://index.rpg.net/display-entry.phtml?mainid=8311 campaign book]] has "[[PowerAtAPrice Power has a price!]]" printed [[Administrivia/YouHaveBeenWarned right on the cover]]. Additional rules include a {{swashbuckler}}-style game, extra IntelligentGerbil races, firearms, cowboys and goblins.

!!Works set in ''Mystara'' include:
* ''TabletopGame/KeepOnTheBorderlands'' -- one of the first ''D&D'' adventures.
[[AC:Video Games]]
* ''VideoGame/DungeonsAndDragonsChroniclesOfMystara'' -- the Creator/{{Capcom}} ''D&D'' arcade-games.

!! This tabletop RPG setting provides examples of:

* AirborneAircraftCarrier: In an adventure ideas section of the ''Dawn of the Emperors'' boxed set, one suggestion is exploration adventures by combined forces of the two main Empires, with Thyatian flying cavalry operating from Alphatian skyships, and some page art depicting the concept. Serraine is a flying city hosting its own airfleet of WWI style wooden planes; both are powered by gnomish {{Magitek}}.
* AlternateUniverse: Mystara is an alternate version of Earth (see also EarthAllAlong and Creator/ClarkAshtonSmith below).
* AlternativeCalendar: The After Crowning calendar and the Alphatian Year, plus seperate calendars for the Dwarves, Halflings, Ylari, Minrothadi, ''et cetera''. Mystara's year has 12 months of 28 days each, no leap years, and solar and lunar calendars in perfect sync.
* AscendToAHigherPlaneOfExistence: The path to Immortality can be chosen by high level Player Characters. Actually, almost every Immortal (see OurGodsAreDifferent) once was a mortal creature. WordOfGod acknowledges that there ''are'' are few well hidden Immortals that never were (it is hinted that they could be resident Old Ones or some other truly Higher power in disguise, Old Ones being to Immortals what Immortals are to mortals).
* BigCreepyCrawlies: The Aranea are a race of 4ft long, 2ft wide spiders with greater-than-human intelligence (minimum Intelligence of 12 in 2e; human average Intelligence in 2e is 8-10) and a powerful affinity for magic and psionics. They're capable of VoluntaryShapeshifting between a singular "humanoid form" that can appear as anything from the size of a goblin to the size of a gnoll, as well as taking a hybrid humanoid/spider form. Though feared as AlwaysChaoticEvil InUniverse, they're actually arrogant, manipulative {{Jerkass}}es at worst, with a typical racial alignment of Neutral. They secretly run the Magocracy of Herath from behind the scenes.
* BigScrewedUpFamily: Several, most prominently the d'Ambervilles, the di Malapietras, the Torions of Thyatis and the Alphatian Imperial Family.
* BizarreAlienReproduction: The Wallaras use this to get around being a OneGenderRace, and would literally only work in a magical world. Once a year, a wallara sheds his skin, after which he carefully bundles it up and places it in his clan's ''tokoo'', a magical shrine. That skin bundle has a 5% chance of being magically transformed into a wallara egg, which hatches several months later.
* TheCaligula: Baron Ludwig von Hendriks. Probably Innocenti di Malapietra too, unless there's a seperate trope for the Borgias.
* CanonImmigrant:
** Blackmoor, the setting of ''D&D'' co-creator Dave Arneson. In 1986 Blackmoor was officially made part of Mystara's history. Apparently, there was a legal obligation to publish Arneson's setting so it was added to the backstory of Mystara.
** As noted in it's own page, ''TabletopGame/KeepOnTheBorderlands'' was moved to TabletopGame/{{Greyhawk}}. ''The Isle of Dread'', the adventure that more or less began the setting, was also imported to Greyhawk in both ''Magazine/{{Dungeon}} Magazine'' and the ''TabletopGame/SavageTide'' adventure path.
* CatFolk: The Rakasta race, of which there are two nations; the British-flavored Bellayne, which happens to be right next to the faux-French Lupin kingdom of Renardie on the world itself, and Myoshima, a feudal Japan-flavored nation of rakasta on Mystara's moon where samurai catfolk ride winged sabertoothed tigers into battle. The species itself originally came in a vast array of sub-breeds mimicking different great cats (for example, the leonic Simbastas), prehistoric cats (such as Rakastadon Fatalis, the sabertoothed tigerfolk), wild cats and house cats.
* ChildMage: Glantri has a few, even rules for [=PCs=]
* CityOfCanals: Glantri City.
* Creator/ClarkAshtonSmith: His stories provided inspiration for the d'Ambreville family, and part of "X2: Castle Amber", the adventure that introduced them, was based in his fantasy-setting of Averoigne in medieval France.
* ColdFlames: The halfling Masters' racial artifact is blackflame: a dark-colored, frigid "fire" that burns inflammable substances and radiates shadow rather than light.
* CoolAirship:
** Alphatian skyships in general and the ''Princess Ark'' in particular.
** ''"[[http://index.rpg.net/display-entry.phtml?mainid=5029 Top Ballista]]"''. Want a NoCelebritiesWereHarmed version of the Red Baron on a biplane armed with two fireball guns and, well, a ballista on top?
** A floating city [[AirborneAircraftCarrier carrying a fleet]] of WWI style planes powered by gnomish {{Magitek}}
** Big wooden birds of prey kept in the air by sacred relics and armed with long-range {{Disintegrator Ray}}s.
** A flying icosahedron (i.e. d20) plated with one-side mirrors.
* DangerousForbiddenTechnique: The Radiance, which may inflict a rotting affliction on the caster. ''So'' forbidden, controversy over its use is what kicked off the Wrath of the Immortals.
* DarkIsNotEvil:
** Diaboli, who look like {{Big Red Devil}}s (only purple), but who are actually a friendly, gentle, peaceful race with a racial alignment of ChaoticGood.
** Hutaakans look sinister, being humanoid jackals, but are not bad people. Just stuffy, culturally naive and rather arrogant as a result of that.
* DeadlyDecadentCourt: Alphatia, Thyatis, and Glantri
* DiggingToChina: Alphatia's solution to the dilemma of how to efficiently access the Hollow World
* EarthAllAlong: Or more accurately, Earth-to-be. The [[http://pandius.com/master-outer-world-colour.png global map of Mystara]] bears a suspicious resemblance to that of [[http://geomaps.wr.usgs.gov/parks/pltec/sc152ma.html Earth 152 million years ago]]. (It also features a solar system with an additional planet instead of an asteroid belt. A planet named ''[[MeaningfulName Damocles]]''... )
* TheEmpire: Thyatis and Alphatia can each fill this role depending on your campaign. The most straight-up evil example, though, are the Heldannic Knights.
* TheEndOfTheWorldAsWeKnowIt: Wrath of the Immortals describes a world-changing adventure there's significant upheval concerning how Radiance is used. It also contains a timeline of events, including regional and world-impacting effects (one of which is caused by a doomsday weapon).
* EverythingsBetterWithMonkeys: Flying monkeys called Tabi are a playable race introduced in ''Creature Catalog PC2: Top Ballista''.
* EvilSorcerer: Bargle the Infamous.
* FantasyCounterpartCulture: Mystara is made of this trope. A ''partial'' list includes: Karameikos (Balkan Slavic, with Byzantine influence from their Thyatian neighbors/conquerors), [[ArabianNightsDays Ylaruam]], Nouvelle Averoigne (Renaissance France by way of Creator/ClarkAshtonSmith), [[UsefulNotes/{{Scotland}} Klantyre]], [[TorosYFlamenco Belcadiz]], Caurenze (Renaissance Italy, Court of the Borgias-style), Bergdhoven (Flanders), Boldavia (Transylvania), [[AlohaHawaii Ierendi]], The Northern Reaches (Scandinavia), Heldann (UsefulNotes/TheTeutonicKnights), Ethengar (Mongol hordes), The Atruaghin Clans (various American Indian cultures), Thyatis (with the Thyatians proper as the classic [[UsefulNotes/TheRomanEmpire Roman Empire]], the Kerendans as the Greek-influenced Eastern Empire, and the Hattians as the [[ThoseWackyNazis Germanic]] Holy Roman Empire), [[AncientEgypt Thothia]], and [[SimSimSalabim Sind]]. ''Many'' more exist in the {{Hollow World}}, Red Steel, and lunar (yes) areas of the setting.
* FictionalDocument: Many, including ''Claransa's Travels to the Center of the World'', the ''Nahmeh'' (Koran-expy), and the ''Poor Wizard's Almanac''s.
* FictionalSport: Alphatians are big-time fans of a team sport called hardball, which is played on a court divided into squares and involves a lot of complicated passing between players.
* FloatingContinent: Features of the Hollow World whose shadows provide the only night under the eternal red central sun.
* FrazettaMan: The Beastmen from the Hollow World, a primitive ancestor-species of common monstrous demihumans like orcs, goblins, ogres, etc, generally fall into this kind of appearance, but sometimes are even more mutable.
* GeniusLoci: The Immortal's DM rulebook states that the home planet is a Megalith, a sentient planet. It is known as Urt, and is about half-way through its active phase. At the end of that phase, it will shed its outer baggage (water, life forms, etc) and enter a dormant phase. Possibly Retconned by the ''Hollow World'' boxed set, as megaliths are implied to be solid inside, not hollow.
* GreenRocks: Cinnabryl from the Red Steel region.
* GrimUpNorth: Denegoth.
* HollowWorld: Literally the name of a boxed set campaign.
* ItRunsInTheFamily: The d'Ambervilles of Glantri, whose first appearance in "X2: Castle Amber" contributed a ''lot'' to the setting's zany streak.
* KillTheCutie: You can't save Aleena.
* LizardFolk: Multiple species of these exist in Mystara. The "common" Mystaran lizardfolk species calls itself the Shazak. Wallaras are an ancient, AlwaysMale relative sometimes known as "Chameleon Men". Gurrash, also known as Gator-Men, were created by the Herathian Magocracy blending Shazaks with alligators in an attempt to create a more useful servant. Results were... mixed, at best. Caymars, or Cay-Men, were a caiman-based repeat of the experiment, who were no more of a success. Krolli are winged Shazaks who favor a mercenary lifestyle. Sis'thiks are desert-dwelling amazonian lizardfolk species, noted for a particular taste for copper dragon flesh.
* LostWorld: The Hollow World is also the preservation area for the Immortals of the setting. And yes, there are dinosaurs.
* {{Magitek}}: Including lots of [[CoolAirship flying vehicles]].
* TheMagicGoesAway:
** The Radiance is used to amplify spell power, at the cost of permanently reducing the global potency of magic (to punish the Immortal Sphere of Energy). As described in ''The Principalities of Glantri'', twenty-five years after the start of the campaign the world will have enough magical drain to prevent spell casting for one day in the year with the drain increasing at certain milestones. If the players succeed in their quest in ''Wrath of the Immortals'', the drain is redirected to the Immortal Sphere of Entropy. If they don't, it's Blackmoor all over again...
** Civilizations that are relocated to the Hollow World generally lose much of their magic, both immediately and over generations, as some types of spell are impossible in the planet's interior and becoming a spell-caster there requires much greater minimum ability scores.
** Special abilities acquired through the use of cinnabryl must generally be forfeited if their users leave the Red Steel region.
* TheMagocracy: The Principalities of Glantri and the Empire of Alphatia. Also the Magocracy of Herath in the far west. Wendar and other elven realms kinda-sorta count here also, given that all the setting's elves use arcane magic.
* MegaCorp: The Minrothad Guilds are organized like a massive medieval-era version.
* MassiveRaceSelection: While most D&D settings have this trope, Mystara has more ''player character'' races than just about any other published setting.
* {{Matriarchy}}: The Kubbits of the Hollow World, perhaps due to worshipping the female Immortal Vanya, are led by their women. Men can hold respected positions and are warriors as well, but the highest leadership ranks in both the military and the culture as a whole are reserved for women.
* MixAndMatchCritters: The Phanatons are a primitive jungle-dwelling race who look like a cross between a raccoon (head, tail coloration) and monkey (body), with the patagia of a flying squirrel added for good measure. They're actually a playable race.
* MonsterAdventurers: Leaving out the various exotic demihuman races, Mystaran sourcebooks presented all of the following monsters as playable character options: Brownies, Redcaps, Centaur, Dryads, Fauns, Leprechauns, Pixies, Pookas, Sidhes, Sprites, Treants, Gremlins, Harpies, Sphinxes, Merfolk, Kopru, Sea Giants, Goblins, Kobolds, Hobgoblins, Orcs, Gnolls, Trolls and Ogres.
* NeglectfulPrecursors: Arguably, the ancient Blackmoor civilization, given their end and the number of their artifacts floating around.
* NinjaPirateRobotZombie: The Kubbits from the Hollow World; dinosaur-hunting miniature human Amazon warriors created by an Alphatian wizard as a race of assassin-slaves.
* NonHumanHumanoidHybrid: The N'djatwa are a race born of systemic interbreeding between elves and ''ogres''. They have the general attractive appearance, mental acuity and magical talents of their elven ancestors, but also the size, strength and stamina of their ogre progenitors. Unfortunately, as both races were darkly pragmatic at best, they're a rather malevolent species, whose culture is founded on slavery and anthropophagy.
* OneGenderRace: The wallara, or "chameleon-men", are an AlwaysMale species of LizardFolk
* OneWordTitle: Also ThePlace, as Mystara is the name of the world.
* OurDwarvesAreAllTheSame:
** They really are. ''The Dwarves of Rockhome'' reveals that their patron Immortal made them this way on purpose so [[spoiler:they'd always be resistant to poison and radiation and have ready-made fallout shelters in case of another disaster like the destruction of Blackmoor]].
** In the Hollow World, they're more likely to be mountain shepherds than miners. This is because, like all other Hollow World inhabitants, [[spoiler:they're an ancient culture placed there to preserve it from extinction. In their case, they're the Kogolor dwarves who lived before the Blackmoor disaster and the remaking of the dwarven race into its present form]].
* OurElvesAreBetter: The standard "high elf" archetype is filled by the forest elves. However, the dark elf analogues, the shadow elves, have chalk-white skin and are ''not'' innately evil (mostly just suckered by a ManipulativeBastard Immortal). Finally, there are the water elves, who are seafaring merchants.
* OurGodsAreDifferent: The Immortals are incredibly powerful beings akin to gods that are ascended from mortal beings. They cannot be hurt by any but the strongest of mortal weapons, they are completely immune to mortal magic, and they can create races and even entire worlds if they want to. The only way an Immortal can be killed permanently is in their home plane -- and you have to have the Immortal's express permission to enter.
* OurWerewolvesAreDifferent: Well, Malachie du Marais is, anyway. And there were some non-standard therianthropes in the Basic rules, especially in the fourth ''Creature Crucible'' supplement.
* TheOwlKnowingOne: The Hisao, a fey race (and potential player character race) introduced in ''Creature Catalog PC1: Tall Tales of the Wee Folk'', are a race of philosopher-priests who happen to be talking, spellcasting owls the size of {{hobbits}}.
* PettingZooPeople: There are a ''lot'' of these:
** Hutaakans, one of the oldest such races in-setting, are anthropomorphic jackals created by the Immortal Pflar.
** Gnolls are humanoid hyenas, and commonly suggested to have been an artificial attempt to duplicate the same process that make the Hutaakans.
** Lupins are a race of humanoid canids, originally appearing as all manner of dogs, wolves and foxes before ultimately being retconned into being just wolf-people. They're commonly reputed to have descended from interbreeding between Hutaakans and Gnolls.
** Nagpas are hideous-looking flightless vulture-men, who appear rather a lot like [[Film/TheDarkCrystal the Skeksis]].
* PintSizedPowerhouse: The Kubbits only stand 18 inches tall, but can reach strength analogous to a better-than-average full-sized man (Strenth 2d6 rather than 3d6) and run so fast that they are no slower than ordinary humans.
* ThePlace: Also a OneWordTitle with Mystara, as it is the name of the world, but the other title, ''Known World'', as well.
* RacialRemnant: The Hollow World section was intended as a way to preserve ancient cultures -- a combination of caverns (allowing for escape), immortal magic (meant to inhibit undead) and subtle manipulation to make residents stubborn concerning their cultural beliefs. If a group is about to die out, the corresponding immortal simply needs to transport a small group inside the shell.
* SchizoTech: Immortal magic causes this in the Hollow World, but not uncommon elsewhere.
* ShoutOut:
** One of the common races of Mystara are doglike humanoids called lupins. An article on lupins in ''Magazine/{{Dragon}}'' #237 mentions a [[ComicStrip/{{Peanuts}} beagle lupin who flies an airplane]] and [[Literature/ArseneLupin a lupin thief named Arsäne Lupin]].
** Dragon Magazine's ''Voyages of the Princess Ark'' series by Bruce Heard, in which Mystara's outlying regions were vastly expanded upon, contained non-stop Shout Outs to everything from ''TeenageMutantNinjaTurtles'' to ''Franchise/StarTrek'' movies to Creator/JohnWayne.
** The Gazeteer ''Elfes of Alfheim'' has three NPC who are easily recognisable [[{{Expy}} expies]] of ComicBook/ElfQuest main protagonists.
* SmallNameBigEgo: The racial flaw of the Caymar; whilst definitely smarter than their Gurrash prototypes, they're nowhere near as smart as they think they are, and are incredibly arrogant, which contributed to their being abandoned as failures by the Herathians.
* SolarCPR: The weakening of magic disrupts the Hollow World's light system.
* SpaceFillingEmpire: Done with the first map ever printed of the planet Mystara, which depicted a major hunk of continent as "the Empire of Dorfin IV", and showed the Empire of Thyatis (whose actual boundaries were much less) encompassing the entire "Known World" region. Averted and Lampshaded by Bruce Heard's Voyages of the Princess Ark article series, which revealed this map to be a complete fraud, perpetuated by a DeadpanSnarker who'd named its various Space Filling Empires after his wife, his mistress, and his dog.
* {{Steampunk}}: Skygnome tech has strong overtones of this.
* TheWallAroundTheWorld: Skyshield keeps the atmosphere in. It has openings on poles and is occasionally breached, which spawns an enormous tornado until the hole regenerates.