So, I have been plagued with the idea of a DnD 3.5 Level 20/20 Wizard/Cleric being Imprisoned in a time when magic was real, and being freed millennia later when magic was a dead idea, no mages or clerics existed, and the world had progressed technologically to a point similar to the current year. 'Fantastic' races were merely myths and legends, mostly put down to be sightings of various currently living creatures in odd circumstances, and people believe magic is merely sleight-of-hand and trickery.
So, we'll begin with a 'How it Happened' exposition. The near-godlike caster was imprisoned by a foe of frightful power deep beneath the earth, in stasis for all time. He was forgotten swiftly, and wars raged on across the world, races fought and died for the same bloodied ground until only Humans remained. Magic died as it was bred out of the race, and the Gods withered and rotted on their thrones without belief to sustain them.
Soon, humans, in all their cunning, began inventing curious devices and instruments to tame the world and bring it to heel, to make themselves the masters of their world. Their technology became near magical in ability, able to transmit information anywhere in the world at the speed of light, able to carry a man faster than the fastest horse for days at a time, able to slay from over the horizon with pinpoint accuracy.
One day, a team of archaeologists find a lost temple to a forgotten god. Inside this temple, they find a scroll written in a language no man has read in millennia. One of their linguists decipher this text, and read it aloud... With a flash, this caster appears in their midst, still partway through a spell to bring ruin upon his enemy. He stops in his action, and surveys these strange men with their curious language and odd clothing. They babble excitedly and confusedly at the appearance of this arcane man in his long, beautiful robes. He waves his hand, and powerful energies seem to warp and twist the very air at his fingertips.
"What year is it?" He asks, his tone curious but authoritative. The words come out clipped and almost mechanically, like he doesn't know exactly what he's saying but he knows to say it.
"It is the year two-thousand and twelve on the Gregorian Calendar in the Common Era." One man says, diplomatically.
"Well, I've only been out for a few years then. What country is this and where might I meet with an authority figure? Kraldor the Vengeful is a terribly powerful creature, and he must be defeated."
"Er. This is the country of England, part of the United Kingdoms. We haven't a king but we have a queen."
"Wait. What is this Gregorian Calendar? It is still the Common Era of Elves, is it not? Was I out centuries?"
"Ahem, what? Elves? The Gregorian Calendar is centered at the end of the BCE, typically considered to end when Jesus Christ died on his cross. I don't... I don't know anything about any elves, mister... Ah, Mister what?"
"I am Avarail, Last Mage of the Corend Empire and High Priest of Pelor, the Sun God." The mage took a curt bow, and asked, "Who is Jesus Christ? Why was he crucified? How do you not know anything about elves? Are you a peasant? Surely you must be a mage of some sort, you freed me from my magical prison easily enough."
The archaeologists conferred for a minute, then turned back to the mage. One stepped forward, the same spokesman as before, and said, "Ah, mister Avarail, it is commonly believed that elves are not real. Nor are goblins or kobolds or any other such mystical creatures of legend. We are not peasants, we are scientists, of a sort. England did away with the feudal system a long time ago. None of us are mages of any sort, though I can do a few card tricks."
The mage narrowed his eyes, and eyed the men carefully. He wove his hands through the air again, casting a minor divination, and said, "Surely there are mages somewhere nearby that I might confer with? And what is a scientist?"
The man eyed him back, openly amused, "Mister Avarail, mages aren't real. Although that neat trick you're doing with the light at your fingers is fascinating, magic isn't real. Scientists are... People dedicated to learning how and why the world works the ways it does. There are many types of scientist. We are archaeologists, concerned with how people of the past lived."
Avarail was blank faced again, and cast another spell swiftly. A small eye appeared above him in the air, and darted out of the room like a shot. For a long few minutes, he was utterly silent, as were the stunned archaeologists. Then, he straightened, a curious look on his face, and said, "Once more, tell me what year it is."
"It is two thousand and twelve CE."
Avarail's control slipped a bit, and his mouth crept open a fraction as he came to realize the enormity of what the man was saying. He swiftly regained control, and smiled kindly at the men. "You men are... Scientists. Men of reason, who do not believe in magic or the supernatural. Curious. And the year is two thousand and twelve. I have been trapped for fifteen thousand years."
The archaeologists scoffed, and the leader said, "Nonsense. Human civilization did not EXIST fifteen thousand years ago."
Avarail got a bright gleam in his eye, and said, "Take me to your 'civilization'. Show me your cities."
---
As this conversation was taking place, a strange thing was happening worldwide. Whole cities and populations suddenly... Changed. Some became lithe, short humanoids with pointed ears, elves of legend. Others shrank to half their height in an instantaneous transformation, becoming vile looking little goblins or somewhat demonic kobolds. Yet others became brutish and strong, green skinned Orcs. Animals of every shape and color changed to new forms. Minotaurs roamed cow fields, Wyverns sprang from tiny geckos and lizards, simple earthworms became vast monsters with acid spit and deadly stinger tails, while yet others were becoming less easily classified creatures.
Deep within the realm of the dead, things stirred. Skeletons and rotting corpses dug themselves up, walking the land of the living once more with malicious intent. Under the sea, fish became whole new races of sentient beings, organizing themselves with their newfound intelligence within hours into vast civilizations. Ghosts and wraiths swept the halls of mausoleums, and some fresh corpses woke up as drinkers of blood.
Within a day, the world was an entirely different place, with a whole host of ancient, forgotten dangers to contend with alongside the modern, mundane dangers.
I'll get into the rest of the setting soon, but for now, this is the beginning.