Boy, let's see here.. where to start.
-- Most of the high level NPCs are either not around in their normal incarnation, or arn't around period. Lord Khelben Arunson is still one of the ruling nobles of Waterdeep, and though his proclivity for the arcane sciences is pretty well known, he is an aristocrat first and foremost (and he leaves his black staff at
home, thank you very much). Elminster is indeed a sage living in Shadowdale. He's quite well versed in a number of topics, mostly magic and history, but he is himself an Expert. He is not hundreds of years old, he was never a woman, and he never banged Mystra. So on and so forth.
-- There was no Time of Troubles. Lord AO did not kick the gods out because three smartasses stole his dayplanner so he couldn't tell who had to be Lord of Taking the Trash Out this week. Gods don't steal profiles or go around killing eachother. They're far less petty in their scope than normal, and are tied to a phenomenon for their power rather than directly being juiced up by the prayers of their worshipers. On the whole, they're much more distant than normal, and if they do interfere with the mortal world, they do so clandestinely. Oh, and nobody's heard of Lord AO - he doesn't exist for all intents and purposes.
-- No Chosen. Of anyone.
-- Parred down the deity list. Many lesser gods were rolled in to the faith of their thematic patron in the form of saints, archangels, sevitors, whatever. The church of Tempus also includes the Red Knight and Valkur, for example. The mulhorandi pantheon did not just boogey on over from earth or anything like that - the gods they worship are the same as the ones the rest of Faerun worships, only wearing funny hats. You call him Lathander, they call him Horus-Re. That sorta thing.
-- Most people don't speak Common. PCs get it for free, NPCs do not - most speak their regional language. If they've got an int bonus or some free skill points and it's appropriate for them to know an international trade pidgin they'll pick it up.
-- Great Wheel cosmology. And none of this region-speciffic nested coterminous planar bullpucky, either.
-- No 18th level ex-adventurer barkeeps, or 11th level wizards leading caravans around.
-- Getting to Evermeet is more than just a matter of sailing in the right direction and asking nicely to dock when you get there - it's not even
here in the traditional sense. And once you go, you never come back. Ever. It's not an elven vacation retreat, it's one step away from the afterlife.
-- Thay has a much more genteel veneer. Much more of an iron fist in a velvet glove, than a festering pit of horrors. Insidious I think would be the word. Enclaves are also embassies, and the servants seem genuinely happy to be so very well taken care of. . .
(now to the more meat and potatoes)
-- The Underdark.. isn't. Under, that is. It's actually another prime material plane. When the Ilythiiri were banished back during the Crown Wars, those doing the banishing didn't screw around. They didn't drive the drow underground, they drive them underground
and thru deep portals into the under-earth of another plane, then shut the door behind them. And you know those other rare-but-wicked underdark nasties like illithids, beholders, and so on?
Guess where they're native to...
Every once in a while when the stars are right, one of the deep portals will open for a time and something may wander thru it, only to once more find the way home shut once the conjunction has passed. Generally speaking, those making the transition don't even notice that it's taken place. Dark stone tunnel, dark stone tunnel, *unknowingly walk straight thru open portal* dark stone tunnel, dark stone tunnel... Suffice it say that getting to the Underdark is a bit more complicated than finding a cave and going down a certain depth.
-- Mythos-type Elder Gods! That's right, great star-spanning minds lie dreaming chaos beyond the deep shores of madness. The Far Realms lie outward and beyond that circle of firelight that makes up the outer planes, in seas of potential rather than chained to actuality. These beings and their childer races are your aberrations and the like, mind flayers, aboleth, and so on (yuan-ti as well).
They're also the primary occurance of psionics. Spellcasting operates on the principle of Pattern + Mana = Effect, and mana is a naturally occurant byproduct of existance. But these ... things.. come from a place where existance doesn't exist, and the only wellspring they have to draw upon to affect the roiling bedlam lies within themselves. Hence psionics. In the realms, psionic ability is almost completely unheard of amongst the normal races, generally only resulting from some naturally psionic being experimenting.
On other worlds (Underdark Prime, Eberron), where the incursion of these beings and their children is more complete, psionics are more common, to the point where normal people can pick up the knack by means of learning to unleash their inner potential. As it stands, the Realms are largely free of such pervasive Elder presence... for now. (The remainder of which has to do with my current campaign plot arc, so I'll quiet up some, heh)
Also related - the Elder Evils (Ithak-Ortheel, Kezef the Chaos Hound, and Dendar the Night Serpent) are themselves cast from that same mythos mold. Dendar is Sseth is Mershalk is
Yig. You get the idea.
Anyway, I'm sure there's more, but it's getting late and that's all I can think of at the moment.
