Acid-Trip Dimension: Limbo, a chaotic realm where the terrain and even the physics changes randomly or at the will of those present.
Adventure-Friendly World: Many of the most popular original settings fit this trope to a "T". Mystara, Greyhawk, and Forgotten Realms are Trope Codifiers. Past the Magitek, so is Eberron (which has several ancient ruined civilizations and just came out of a continent-spanning war).
Alien Geometries: The most significant example is found in Basic D&D's Immortal Set. The game describes up to 5 dimensional planes, giving rules for how they work. They also describe that mortals exist in three dimensions, immortals exist in four, and Old Ones exist in five. In addition, normal mortals exist in dimensions 1, 2, and 3 while mortals from the nightmare plane exist in dimensions 3, 4, and 5.
Anachronism Stew: Despite the typical D&D environment being a medieval Europe pastiche, various settings have included dinosaurs, a god of cowboys, Eastern martial arts, and many more... plus a few that can't be justified by Rule of Cool, like the lack of gunpowder despite the availability of other weapons that came long after the invention of firearms.
Barred from the Afterlife: Module I3 Pharaoh. The pharaoh Amun-re sacrifices the wealth and well being of his people to build himself a magnificent pyramid tomb.When he's threatened by an angry mob, he lays a curse that will cause the land to dry up if he is killed. A member of the mob kills him anyway, and the god Osiris is forced to carry out the curse. However, he punishes Amun-re by condemning his spirit to wander the land until someone steals his treasure from his tomb.
B2 Keep on the Borderlands. The minotaur has a cave complex inside the Caves of Chaos. Its caves have a spell on them that causes intruders to lose all sense of direction.
S4 The Lost Caverns of Tsojcanth. Somewhere in the Caverns is a teleportation trap that sends victims to other planes of existence. One possible destination is a giant labyrinth with two minotaurs riding bulls. They will hunt down and kill anyone inside the maze.
Behemoth Battle: The module WG7 Castle Greyhawk. On Level 5 there's a battle between an Apparatus of Kwalish and an iron golem piloted by an orc. It's a parody of FASA's BattleTech game (the orc is even named "Fahzah").
Many 3rd Edition spells have a self-explanatory [Evil] descriptor. Necromancy magic in general plays this role in the Ravenloft campaign setting.
Arcane casters in the Dark Sun setting can choose to be "Defilers", which allows them to reroll the results for any spell they cast at the cost of further desertifying the world, or at least the portion of it they're in. This makes them about as popular as witches were in 17th century Salem, MA.
Bloody Bowels of Hell: Layer six of the Nine Hells of Baator is Malbolge, formerly a boring place of boulders rolling down an eternal slope, ruled by the Hag Countess, who wasn't even a real devil. Then came the Fiendish Codex II, when the Countess was replaced by Glasya (daughter of Asmodeus himself), who did some remodeling. Now Malbolge is largely made up of its former ruler and sports distinctly fleshy terrain, with tall oily hairs instead of forests, lakes of bile and viscera, and ivory towers that used to be fingers or ribs. Special mention must also be made of a great mound at the layer's center called the Birthing Pit.
Bloody Horror: Module X2 Castle Amber. One of the castle's features is the Blood-Stained Arch. A steady patter of blood flows from the underside of the arch, with no apparent source. The blood is in atonement for all of the bloody crimes committed by the Amber family.
Body Horror: Pretty much the entire point of the "Book of Vile Darkness" and especially the "Libris Mortis." A fair number of psionic abilities in 3.5e invoke this as well - including one which causes the target's skin to grow into a single solid membrane, effectively immobilizing it.
Let's not forget Lords of Madness (with many "eldritch horror" elements), Fiendish Codex I: Hordes of the Abyss (with some truly foul concepts for demons), and Elder Evils (with some lovely beings such as a world which is actually the undead fetus of a god and an enormous 1-mile wide bloated mass of corrupt proto-life that tries to mutate all life on a world to be like itself). One admires the creativity shown in these books... and questions the minds that came up with these ideas.
What happened to the hag countess, also what usually happens to those who die on the 6th layer of hell. Their body fuses with the layer, their souls however stay where their body is. Its such a painful fate that those unfortunate enough to suffer it tend to go mad in a matter of hours.
Cain and Abel: The sibling gods Heironeous and Hextor function as pretty much this on a divine scale.
Circling Vultures: Module B8 Journey to the Rock. When the PCs reach the Cave of Sanctuary they will see sinister vultures circling lazily overhead: they're about to snack on the body of a recently killed gnome.
Clever Crows: Ravens are commonly found as wizards' and sorcerers' Familiars. Raven familiars always have the ability to speak.
Clip Its Wings: 1st Edition Dungeon Master's Guide. Flying creatures with wings will be unable to fly if they take too much damage, due to their wings being a prime target for enemy attack.
Clone by Conversion: Third edition introduces the psionic power "Mind Seed" which, after a week-long incubation, turns the target into a mental duplicate of the psion (though eight levels lower than the psion when s/he infected the target).
Dark World: The Plane of Shadow in 1st and 3rd Edition; the Feywild and the Shadowfell from Fourth Edition.
Deadly Dust Storm: Modules I3-I5 (Desert of Desolation series). One possible random encounter while in the desert is a dust storm. There's an 80% chance of the PCs getting lost unless they immediately halt, and movement rate is cut in half if they continue. The storm lasts 3-22 turns (30 minutes to 3 hours 40 minutes).
The Far Realm contains an infinite number of layers, these layers range from inches thick to miles, and it is often possible to perceive multiple layers simultaneously. These layers can grow, spawn further layers, breathe and possibly die. It has toxic natural laws and the laws of most of the regular settings are in turn toxic to most of the residents of the Far Realm. The Far Realm is literally outside of reality as mortals understand it.
An "older multiverse in which the rules were very different." This place is no longer around, its only legacy being some aberrations.
Xoriat is a plane similar to the Far Realm located in the Eberron campaign setting.
The Abyss appears in several of the campaign settings as the home dimension of demons. It is divided into so many 'layers' (regions) that mortals have never counted them all, although legend claims that there are 666, each larger than a planet. In addition to some fairly standard fire-and-brimstone regions there are sections of the Abyss infested with flesh-devouring mold, one region that is nothing but an utterly bottomless void, and some where the ambient evil instantly reduces mortals to husk-like undead known as bodaks.
Elemental Plane: There are many of these. The "inner planes" include planes of Air, Earth, Fire, and Water, as well as the planes of "Positive Energy" and "Negative Energy".
In the Planescape setting, the "outer planes" include a plane representing each of the Character Alignments, and the "inner planes" also include "quasielemental" or "paraelemental" planes such as "the Plane of Dust", "the Plane of Lightning", etc.
Module WG7 Castle Greyhawk. The Queen of the Honeybee Hive on level 7 opened a gate to the Demi-Plane of Flowers, a gigantic plain covered with every imaginable type of flower and plant.
4th Edition takes the elemental planes and mixes them into one plane, the Elemental Chaos.
Elves vs. Dwarves: Alternately played straight, subverted, or averted altogether depending on the setting.
The most prominent examples that span those editions are the clerics of gods who are patrons of forces such as entropy and chaos. Unsurprisingly, almost all of these gods (and their clerics) are some flavor of evil.
In 1st Edition, the psionic science Dimension Walk was used to move through various dimensions and end up back in the Prime Material Plane a considerable distance from where you started. Using this power allowed travel at a rate of 21 miles per ten minutes (126 miles per hour).
In 1st and 2nd Edition a character could enter the Ethereal Plane, move at tremendous speed to another location corresponding to a particular place on the Prime Material Plane, then leave the Ethereal Plane at that place.
1st/2nd Edition Greyhawk Adventures supplement. The deity Istus could use her Spindle of Fate to cast a Web of Stars, which sent the targets to another plane of existence. Once there, a creature that knew the way could travel the Web and arrive at any desired location.
2nd Edition Forgotten Realms Adventures supplement. After reaching level 10, specialty priests of the deity Bhaal could use the ability Plane Skipping. This involved traveling to Bhaal's home plane of Gehenna, moving an appropriate distance on Gehenna and then returning to the priest's original plane. Each 10 feet the priest moved on Gehenna caused them to return 1 mile away from where they started from. The entire trip took about 20 minutes plus the time necessary to move the distance on Gehenna.
The 2nd Edition spell Shadow Walk allowed the caster and any creatures he/she touched to partially enter the Plane of Shadow. This allowed them to move at a speed of 7 miles per 10 minutes (42 miles per hour) with regard to the Prime Material Plane. When the journey was completed, they could return to the Prime Material Plane at the desired location.
The "Dimension Door" spell is a line-of-sight teleportation spell whose name suggests that it works this way. And one version of the fluff text for teleportation in general states that all such spells work by jumping in and out of the Astral Plane.
Fantasy Kitchen Sink: The standard Monster Manual includes entries for vampires, fairies, dinosaurs, zombies, genies, angels, demons, plant creatures, Frankenstein's Monster (in the form of flesh golems)... and that's not even getting into all the supplements. Of course, Dungeon Masters can selectively choose which creatures to include in their campaigns.
Taken to a new level in 3E and 4E with templates that can be added to several creatures. Yes, that means you could, in theory, have a fiendish half-dragon vampiric dark elf.
Field Power Effect: Various spells that boost and nerf groups of characters, such as Bless, Hallow and Unhallow.
Fungus Humongous: Multiple examples, with Zuggtmoy being the demonic queen of them all.
One of the setting's nastier abominations is Atropus, the world born dead, a planet crawling with undead whose arrival in a system heralds disaster and that only leaves dead worlds in its wake. It's fairly consistent that it's the remains something huge and (un)dead, but its exact nature varies — sometimes it's an enormous atropal (the undead corpse of a stillborn god), while other times it's the head of a colossal primordial being.
The current incarnation of the sixth layer of Hell, Malbolge, is formed out of the corpse of its former ruler, Malagard the Hag Countess. Its mountains, for instance, used to be the Hag Countess' bones, and there is a tunnel that used to be her throat that still contracts and expands rhythmically.
The Githyanki capital of Tu'narath is a metropolis built on — and into — the colossal, petrified corpse of a forgotten god, adrift in the timeless Void Between the Worlds of the Astral Plane.
Glowing Flora: Glowing fungi and lichens appear in the underground settings of several 1st Edition AD&D adventures, including D1 Descent Into the Depths of the Earth, D2 Shrine of the Kuo-Toa, Q1 Queen of the Demonweb Pits and A4 In the Dungeons of the Slave Lords. They are included to make it easier for PC adventurers to see if they lose their artificial light sources.
Going to Give It More Energy: In most editions, anyone on the Positive Material Plane heals a set number of hit points per round. This can even raise the amount above the normal maximum... but if said creature reaches twice its HP total, it immediately bursts into energy and is destroyed.
Actually, it has to fail a Fortitude save to explode. But since a natural 1 is an automatic failure, even the sturdiest creature will fail its save sooner or later...
Gold–Silver–Copper Standard: D&D is one of the early trope codifiers. Prices are usually listed in g.p., unless they're small prices, in which case they're listed in s.p. or c.p.. The exchange rates were as follows:
A Handful for an Eye: In the Dark Sun/World of Athas setting, gladiators are trained to use dirty tricks in combat, such as throwing sand in an enemy's eyes.
Hellfire: Made by Devils, and can burn creatures that are made of fire.
Hell Invades Heaven: If the Blood War between the demons and the devils ever ends, the Upper Planes can look forward to a full-scale war with the fiends as they launch an invasion. When the Blood War did end in the Forgotten Realms setting...this didn't end up happening.
Holy Is Not Safe: The Positive Energy Plane serves as the power source behind "holy" damage spells and abilities that Turn Undead, but any living being who tries to enter the plane without appropriate protection will find their bodies being overloaded with life energy and risk being vaporized if they spend too long there. Ironically, according to 3.5E Rules as Written, undead that travel to the plane simply gain (temporary) hit points, and are immune to all the downsides.
Hot Skitty-on-Wailord Action: Several species in Dungeons & Dragons are quite capable of breeding with just about anything. In 2nd Edition, goblinoid species were specifically cited for fecundity and adaptable with most other races, while elves were specifically noted to choose whether or not they could reproduce with any given partner in The Complete Book of Elves. 3rd Edition carried this further; dragons were capable of offspring with nearly anything alive, while aasimar and tieflings all have celestial or infernal ancestry, respectively (it helps that shape-changing abilities are common amongst the respective parentage). Further parentage was possible; the number of templates for half-parentage is astounding. The Book of Erotic Fantasy actually has a table for this kind of thing. It once appeared on /tg/, with big red arrows pointing to the part where one-inch-tall tall sprites and twenty-foot-tall cloud giants could interbreed, bearing the tactful message "WAT".
There's even a 3.5 sourcebook of half-breeds based around this trope... covering everything from the slightly unusual (human/merfolk) to the completely bizarre (elf/giant eagle).
Human Sacrifice: A tradition among the evil religions, though some have it in a less formal manner. Gruumsh, the god of slaughter and pillaging, gets his sacrifices through said slaughter and pillaging, so not so much of the high priest hacking off some virgin's head.
Just Before the End: Mayfair Games' Role Aids supplement Lizardmen has an alternate dimension consisting of a vast plain dotted with the ruins of ancient cities under a dim sun dying of old age.
Level Drain: As D&D made the Class and Level System, so also did it make this. Undead such as wraiths had the power to take your levels away, often forcing you to gain them back the hard way. Although it was eventually phased out.
Loony Laws: In the adventure X3 Curse of Xanathon, the title curse causes the Duke of Rhoona to proclaim several odd laws, such as "All taxes must be paid in beer", "All riders must sit backwards on their horses" and "Horses can only be fed meat".
Magic Missile Storm: Magic missile is the obvious example and the Trope Namer, but there are many other spells consisting of a barrage of magical projectiles or beams. For so basic a spell (it can be learned by 1st level arcane spellcasters) magic missile is an extremely versatile weapon (due in large part to being incapable of missing, but also because it does force damage which is effective against incorporeal beings), and there's a number of builds that are designed around maximizing its potential. Flavor Text from the D&D Wiki article for one of them, Magic Missile Stormer, provides the page quote.
Mistaken for Quake: The module series "Desert of Desolation". While in the desert the PCs can experience an earthquake as a random encounter. In fact it's caused by the passage of a large number of Sand Worm type creatures called "thunderherders".
Monster Munch: Basic supplement GAZ1 The Grand Duchy of Karameikos, adventure "Toys of the Madman". The PCs and a few NPCs are kidnapped and placed in a dungeon. Some of the NPCs are there to be killed and eaten by monsters to show the PCs what they're up against.
Moving Buildings: Stronghold Builder's Guidebook has locomotion as a feature for a fortress as an option. how fast and what kind of movement depends on what your willing to pay.
Mystical High Collar: A lot of art shows wizards, witches, and other supernatural characters wearing high collars.
Mystical Plague: In 2E, the wizard spell Contagion from Player's Handbook infects one subject with non-virulent disease, and the cleric spell Breath of Death (reversed Breath of Life) from Tome of Magic affects an entire community. Anyone who fails a saving throw vs. death magic is infected with a disease that is fatal in 1-6 weeks.
In 3E, Contagion remains a core spell and is given to clerics as well.
National Weapon: Many deities have a preferred weapon that their followers tend to use. For example, the holy symbol for Kurbag is a double-bladed axe. In 3E, the Spiritual Weapon spell summons a weapon made of pure force that is described as taking the form of the user's deity's favored weapon (or a form specific to alignment for characters without a deity).
No Conservation of Energy: Though surprisingly averted in first edition, this trope is played straight in the Mystara setting: The Radiance, which is a major source of magic for a small secret cabal in the Principalities of Glantri, gradually and permanently drains the magic of the entire world each time it is used. This is because all the Immortals decided it would be too dangerous to the balance among the Spheres to allow such an easy path to Immortality in the sphere of Energy, so they altered the Nucleus of the Spheres, the device which generates the Radiance, to draw power from the Sphere of Energy, thereby giving the Immortals of that Sphere a strong incentive to regulate its use. It didn't last.
The shadow elves' version of the Radiance is kept secret, and averts this trope — its only negative effect is crippling newly born babies in the future.
Not-So-Safe Harbor: The pirate port of Scrape in the Magazine/Dungeon magazine #16 adventure "Vesicant".
Power Glows: Magic weapons will often glow without any modification to their base price. There are also a few notable examples:
Although optional in previous editions, several 4th edition paragon paths actually have glowing weapons as paragon path features.
Angelic Avengers take it further; their entire bodies can light up.
An entire series of cleric spells and psionic powers in 3.5 allow you to charge up power in your body and then shoot it as laser beams. As long as you haven't exhausted your stock of energy blasts, you actually function as a 60-foot light source, the color of the light being determined by how powerful the spell is you're using.
Also the Nimbus Of Light feat and its improved version from Book of Exalted Deeds.
Paladins in Pathfinder can imbue their weapon with a divine spirit, granting it magical properties depending on level and causing it to light up like a torch.
A lot of the illustrations in 4E PHB 2 & 3, specifically Divine and Psionic characters.
Projectile Spell: A wide variety, ranging from the plain Magic Missile, to ones with specific forms such as Color Orb.
Psychic Powers: Originating as substitution powers in Eldritch Wizardry of all places.
In 2nd edition, the psionicist class and a chance of possessing a wild talent for characters of any class. Except Dark Sun where everyone has at least a wild talent.
3rd edition has the psion, psychic warrior, soulknife, wilder, ardent, divine mind, lurk, and erudite all as base classes. If you go to third-party books, even more exist.
4th has introduced psionics as a power source in the Player's Handbook 3. The psionic classes (thus far) are the Psion, Monk, Ardent, and Battlemind.
5th edition has a different take on psionics, at least for now. Spellcasting enemies from the 5E Monster Manual labeled as psionic don't require spell components in order to cast spells. The July 2015 Unearthed Arcana article reveals playtesting for the Mystic class, something of a replacement for all the psionic classes.
Religion of Evil: Most of the evil-aligned gods have churches like this, which may end up being a stock opponent for the PCs.
Rerouted from Heaven: In the module A Paladin In Hell, during the funeral of a powerful paladin, the entire temple hosting the service is dragged into hell to claim his soul. The players have to travel to hell, find the temple and free his soul. Oh, and the module was close to Tomb of Horrors in terms of unfair difficulty.
Renegade Splinter Faction: In the 2nd Edition supplement The Complete Druid's Handbook has the The Shadow Circle. A secret society within another druidic order, the Circle use evil methods to enforce their radical beliefs.
In early editions, there was a potion that could make clouds it was poured onto solid.
Module WG7 Castle Greyhawk, Level 4 "There's No Place Like Up". If the PCs climb up a magical rope, they can walk on solid clouds floating high in the air.
Deities And Demigods Cyclopedia
The Chinese mythos deity Chih Sung-Tzu rides a storm cloud that can support up to ten beings of any size.
The Japanese mythos deity Susanowo can often be found riding a storm cloud.
In the Sumerian mythos, all of the deities have clouds that they can ride on. The clouds can teleport to any place that has clouds in the sky, are immune to all attacks and can carry anything the controlling deity wishes.
Standard Fantasy Setting: The main guides present the setting like this. People can design their own campaigns however they wish, so a basic template is handy. The official campaign worlds all diverge from it to a greater or lesser extent.
Vancian Magic: A hallmark of virtually every version of the game except for 4th edition.
Partially back in 5th edition. Spellcasters still have limited spell slots, but don't need to assign spells to specific slots.
The War Just Before: Basic D&D module CM4 Earthshaker. In recent years the country of Stamtral has raided the PC's country Vyolstagrad several times, but the two nations are currently in an uneasy peace. If the PCs don't play their cards right another war could break out as a result of their actions.
Weird Weather: Module I12 Egg of the Phoenix. While the PCs are traveling from the Crypts of Empyrea back to Nimbortan they will encounter a brief bizarre storm. It starts with a gale force wind, continues with rain that is almost boiling hot, then changes to razor-sharp sleet that slices exposed flesh and clothing to ribbons. Not to mention Hostile Weather while they take the egg back.
Whatevermancy: Notably, the core rules from 1st to 3rd edition only uses this form for the school of Necromancy. But if you look around, you'll also see an abundance of references to pyromancy, cryomancy, geomancy, chronomancy, cerebromancy...
In 4E, there is no longer such a thing as an Always Lawful Good race, but there are tons of Always Chaotic Evil. Metallic dragons and other good creatures are now Unaligned (neutral), and many formerly neutral ones are now mostly evil. Good is a very, very rare individual choice. (Although any creature can make that choice now; almost nothing in 4E is "genetically" evil.)