You asked for it. Start with the basic Dungeons & Dragons setting, which contributed to the basic ideas of the High Fantasy genre as we know it today, Dwarves, Elves, Dungeons, Dragons, et cetera. Then something completely unprecedented happens: the moon grows in the night sky, until it is literally falling to the earth, particle by particle, in a series of apocalyptic meteor showers every night. Civilizations crumble as untold numbers of lives are lost in the nightly lunar rains, showers of boulders raining down on the land like some unholy siege. The survivors flee underground as the only effective shelter against the cataclysm.
This is where it gets weird. First, it turns out the moon is inhabited. All sorts of alien monsters are brought down to earth, voluntarily or not, as part of the lunar rain. The most feared among these are the Lunar Dragons: all-consuming monstrosities which are, pound for pound, more powerful than any terrestrial dragon. Worse still, Lunar Gods are coming into contact with the earthly deities, and waging war against them. Clerics and Paladins find that they occasionally simply don't receive the magic usually granted by their hosts, as the gods are weakened or at least kept busy by the war. Second, one dwarf mechanic from an ancient guild of mechanics introduces something long-lost to the world: steam-powered Humongous Mecha.
Yes, you read that right.
The result is that the safest places on the planet, besides deep underground, are now the City Mechs, obscenely huge, humanoid mechs that carry entire cities on their backs.
This RPG campaign setting provides examples of:
- An Adventurer Is You: It's a D20 setting, you do the math.
- Alien Invasion: The things coming down with the chunks of the Moon, killing anything unlucky to be in striking distance once they land.
- BFS: Well, any sword used by large scale mech count. The biggest one is the Moonquencher, a sentient magic sword used by Sharlorn, the Necropolis mech. It's mentioned that its creator already has plans for an even larger sword.
- Anti-Magic: A limited form of this is what makes the lunar creatures so dangerous. The lunar creatures take only half damage from any element except for earth, from which they take double damage.
- Caped Mecha: Mentioned and deconstructed for laughs in the Paladin profile."One Legion commander even commissioned a massive velvet cape for his paladin, although an encounter with a flame nozzle nearly led to disaster two weeks after the cape was installed."
- Clap Your Hands If You Believe: The cult of Dotrak, a machine god, is bringing Dotrak into existence.
- Clock Punk: While Steampunk is more common, the vessels of Dotrak gain a clockwork heart, and a handful of mechs (most notably Smiggenbopper's Perambulatory Orc) use clockwork rather than steam or magic. Even the clockwork mechs are wound by a steam engine though.
- Colony Drop: The Lunar Rain, formed as the moon falls to earth piece by piece in constant, devastating meteor showers.
- Cybernetics Eat Your Soul: The "steamborg" class has a trait called "Lose Self" that forces a Charisma check to avoid spending the day as a partially biological machine.
- The Dreaded: Elves normally don't thrive in the Dragonmech world, but they have the invincible mech Tannanliel which is so feared that it affects entire faction politics.
- Eldritch Abomination: The lunar gods are weird. The good old D20 Aboleth also exist here, and, worse, now they use mechs to travel on land as well.
- The End of the World as We Know It: It's kind of hard to miss the descending moon. It's already totally redesigned the face of the planet and it hasn't even hit yet.
- Eternal Engine: The lower levels of the city-mechs are filled with "gear forests," enormous rooms of engines, pipes, gears, and other machinery. They have even developed their own ecosystems, with the grease lizard being the dominant predator. One of the variant classes introduced in DragonMech, the clockwork rangers, (essentially rangers dedicated to preserving the gear forests) is actually specialized for moving in this kind of environment, having developed skills and abilities that let them navigate the gear forests with ease.
- Fantastic Racism: Shar Thizdic, the master of the Legion and a diehard human supremacist. Since the Legion is one of the most powerful military forces in the world, this has made a lot of people very worried.
- Feel No Pain: Tortogs are largely immune to pain unless someone punches through their shell.
- Impossibly Graceful Giant: The mech devil prestige class, a sort of monk/barbarian/mech pilot hybrid, gains a supernatural ability that turns their mechs into the kung fu robot subtype.
- Invincible Hero: The elves' city mech Tannanliel is a force of good that has curbstomped every enemy it has ever encountered.
- Instant Awesome: Just Add Mecha!: All kinds of mecha are available (except those with modern technology) and in various places the ecology and the setting's planar cosmology is starting to change because of the existence of mecha.
- The Legions of Hell: Due to fact that the gods of Highpoint are weakened, even weak devils can be found here.
- Lizard Folk: An unusual form in tortogs, tortoise-men who serve as traders because they can withstand the lower intensities of lunar rain thanks to their massive shells.
- Magitek: The animated mechs, including undead mechs created via necromancy. There is also spell furnance, which function just like steam engine except it's magic-powered.
- More Dakka: The elf mech Tannanliel relies on an arsenal of cold, fireball and lightning wands for its weapons. Lunar creatures take only half damage from these and none if they make a saving throw so these weapons shouldn't pose a threat, but Tannanliel carries hundreds of these wands and from sheer weight of that firepower the mech has annihilated every lunar creature encountered.
- Nay-Theist: Everywhere. Something about the gods failing to stop the freaking moon from falling kind of turned a lot of people off the whole "religion" thing. Ironically, Mech Manual states that the orcs are still faithful to the gods. They view the lunar rain as an act of their gods, and the gods' failure to respond to their prayers is only a passing concern, as even the greatest warriors must rest after a hard battle.
- Our Dragons Are Different: The local ones are relatively standard D20 dragons. Lunar dragons, on the other hand, are bulky monsters with horns all over their faces, pallid and veined skin, weakened flight in terrestrial gravity, no interest in treasure, and More Teeth than the Osmond Family.
- Powered Armor: Used by the Irontooth Clan and Orc.
- Rule of Cool: If you couldn't tell by the description.
- Scenery Gorn: Every description of the surface world emphasises that the lunar rain has kind of messed up everything everywhere. Natural beauty is so hard to find that kings will pay a fortune for a bunch of daisies.
- Science Fantasy: Steampunk + High Fantasy.
- Spider Tank: The Scorpion. Mech Manual add Ganasher, Lactrodectus (a literal example) and Deep Spider. Finally, The Last City add Nardigrum to this trope.
- Sturdy and Steady Turtles: The tortogs are humanoid tortoises notable for their ability to Feel No Pain from anything that doesn't punch through their very thick shells — and it takes quite a lot to break their shells. This has resulted in them becoming an entire species of smugglers and traders in the setting's present, as they're the only ones capable of withstanding the agonizing rains of micrometeorites that pelt the world on a nightly basis and forced almost all other species to retreat underground or inside city-sized Giant Mecha.
- Title Drop: The DragonMechs are a Stenian elite mech unit dedicated to slaying lunar dragons.
- Took a Level in Badass: The core rulebook only gives passing mention to orc mechs and undead mechs. The first is a primitive design and not very good in battle, while little info is given about the latter. Then in Mech Manual it's revealed that the orcs are now capable of building their own series of mechs, and some are extremely dangerous. It also states that while undead mechs are uncommon, they aren't as rare as they used to be. And there is even a Necropolis, an undead city mech.
- Transhuman: The entire point of the steamborg class, who replace their meat parts with steam-powered machinery. The Assimilated prestige class achieves a variant by permanently installing themselves into their mechs.
- Weird Moon: Populated by strange monsters and eldritch abominations, and oh yeah it's falling, did we mention that?
- When Trees Attack: Forestrati are treants driven insane by the ongoing apocalypse, which randomly attack anything that moves.