RamblySettingIdea

Okay, so this will be slightly rambly since I have come up with this literally today.
It basically started with my interest in "modern day but weird" settings.

So, I had this idea that there were parallel universes, where the rules there may or may not be the same as our Earth.  I have them separated roughly into three groups.

The first group is "basically Earth with minor variations."  A world where you're eating corn flakes instead of cheerios for breakfast because corn flakes were on sale isn't very interesting, but it is different.

The variations don't have to be that minor.  They can still be drastic as long as the rules of physics and such don't change.  Lincoln could have lost the election.  Alexander the Great could have taken over the world.  A dog could have chewed a hole in your pants on the way to work.  All of those belong in this group.

The second group is where the rules aren't the same.  Wizards could exist.  FTL travel might exist.  Dogs might be intelligent.

The third group is subjective, wherein it's similar to the second group, but it's very different from person to person.  I'll need to go into this after I describe the people who can see into these other alternate universes.

So, in this setting, anyone who is a lucid dreamer can peer into these other universes.  Lucid dreaming is not, in fact, taking control of your own dreams but peering at your other self in those universes.

Most people who are lucid dreamers will gain nothing from this or even realize it's unusual.  You're not going to learn anything new from other you that is only different because he likes fruit loops more than fruity pebbles, which we all know is a crime.

Most that can access that second or third group of universes lucid dream their way into a first-universe where they are different in a noticeable way.  Like, instead of someone going to college for a writing degree, they went for a music degree.  And then, when they wake, they can play the guitar better than before.

Then with a bit of practice and a lot of time, they can drift their way into that second group of universes, where they can learn new, more interesting things at the cost of identifying with versions of themselves that aren't as much themselves.  Like, you might find a version of yourself that is a wizard, but he's a foot shorter, bald, and hates chocolate. Or something even more severe than that, but nothing truly inhibiting.

Some people might be unfortunate to dream their way into a second universe situation without the gradual lead-up from the first, but people don't tend to learn from those, thinking that they probably shouldn't have eaten that shepard's pie before going to bed.

The third degree of alternate universes, then, is where the difference is so different from the you that you know that it's really jarring and difficult to deal with.  Sometimes it's in a less fantastical way, like a Dr. Jekyll and Mr. Hyde scenario where the other you is so different personality-wise that you can't identify with them.  Or maybe they are just different in a fantastical way, like alternate-you being a female elven bard with a penchant for baking cupcakes.

Third degree alternate universes are dangerous for another reason, which I will go into in just a sec.
So, even with people who are lucid dreamers who never get anything interesting new knowledge-wise, they still can recognize and use (if they know how) artifacts from the alternate universes.  If someone brings a vorpal sword from another universe, they can still lop off heads with it.

With practice, time, and a bit of luck, people who can visit those other degrees of universes can bring or make artifacts from those other universes in our Earth.  And as long as you don't try and point them out to non-lucid dreamers, they will generally ignore them.  If you just go on a rampage throwing fireballs in a bowling alley, people will notice, and down that path lies madness.

The third degree of alternate universes is most dangerous, though, as nightmares can come from those.  Truth be told, they can come from second universes, but the dreamer can maintain their hold on the dream well enough that it's not a serious risk, unless they let their judgement lapse.

Third degree separation universes can produce those nightmares, though.  Called as such back in olden times, these creatures (not necessarily nightmarish-looking) can come of their own accord to our Earth, and they get no such protection of being ignored by citizens.  Obviously, anyone in the know wants to prevent these from getting loose.

So, obviously a Dresden Files-esque story would be the obvious choice, running around and finding loose nightmares or people misusing their powers.  After all, a charm spell that normal people don't recognize being used is still just as effective.