This is a story I came up with. Hope you guys like it!
Mabel: Hey Dipper, have you always wanted to know what it would be like if the world was different?
Dipper: I don't see how that's possible. Then again, why did I just say that in Gravity Falls?
Mabel: It might be. I mean, just think. Pacifica and Gideon are good but me and you are the evil ones.
Dipper: Ha! I'd still try to stop Gideon if that were to happen!
Mabel: Actually, I wouldn't mind going on another date with Gideon if that were to happen.
Dipper: What!? Come on, either way, there's no possible logical way we could actually just find a device and we can just simply enter another universe.
Mabel: Didn't that happen when we found that one room?
Dipper: Yeah, but I'm not keeping my hopes up.
Soos: "from the background" Hey dudes! I found a device that I think could go into other universes.
Dipper: "to himself" Stupid deja vu.
"theme song plays"
Soos: So, I was cleaning up, and in the parlor, I found this weird contraption. It's super bonkers creepy!
Mabel: "sees the contraption" Whoa, cool!
Dipper: I wonder if it still works. "presses button and a portal opens up"
Soos: I wouldn't mess with it if I were you...
Mabel: What's the worst that could happen? "enters portal"
Dipper: Wait, Mabel! "goes in after her"
Soos: Hmm. Maybe there isn't anything suspicious about this machine. "exits room"
Mabel: (in the portal) "exits the room" "looks around" Hey, this looks exactly like the Mystery Shack.
Dipper: I think this might be, Mabel. "walks down the hall and into the twins bedroom"
Mabel: Let's go downstairs. Maybe us versions are doing something in the living room or something. "goes downstairs"
Dipper: "looks in drawer of their bedroom and sees 3" Hmm. Maybe there isn't anything strange going on. "hears squeaking" Um, what was that? "sees Cheekums come out from under "Mabel's" bed" Wait, isn't that Gideon's pet? Wait a minute, that means...nah. "goes downstairs"
Mabel: "yells to Dipper" Hey Dipper, check it out!
Dipper: "sees Mabel talking to what looks like themselves but it's really Good Pacifica and Good Gideon"
Mabel: Apparantly, I'm blonde in this universe! How cool is that?
Good Pacifica: I think we could be good friends!
Mabel: Yeah, like Grenda and Candy.
Pacifica Pines: Who are they?
Mabel: "laughs nervously"
Dipper: Hey, um, 'Dipper'? Can I talk to you in the office?
Gideon Pines: Sure.
Dipper: "takes him up to the office" "yells" Don't think I know who you are!
Gideon Pines: Wait, what?
Dipper: I know you're playing tricks with me and Mabel's minds, Gideon Gleeful!
Gideon Pines: ...who are you talking about?
Dipper: Don't act dumb! If you're really not Gideon that I know, then do you know about this? "takes out 3"
Gideon Pines: Yeah, I do.
Dipper: Oh, really?
Gideon Pines: No, I'm serious, I do! I even know about the gnomes, manotaurs, clones, and other things that have been going around in this town. You must be from another universe, which is intriuging.
Dipper: So, if you're nice in this universe, then that means that girl that Mabel is friends with now, is, my guess, Pacifica?
Gideon Pines: Exactly.
Dipper: Ok then, but then where's mine and Mabel's versions?
Gideon Pines: I guess that means, they are the evil ones.
Dipper: Actually, Mabel doesn't know that it's Pacifica she's talking to.
Pacifica Pines: "screams" "a door is heard slammed"
Gideon Pines: I think she has now...
"Dipper and Gideon enter the twins' bedroom to see Mabel running after Pacifica"
Mabel: Who are you?! What have you done with my counterpart and Waddles?! "sees Dipper" Dipper, I'll save you from this bodyswapping witch!
Dipper: Mabel, wait! She may have a different name, but she has the exact personality as you! In a way, Pacifica is you in this universe.
Pacifica Pines: Boy in the pine tree hat is right.
Dipper: Uh, actually, my name is Dipper.
Pacifica Pines: Oh ok.
Mabel: Ok, I'm a little confused and a little better now. Sorry for attacking you.
Pacifica Pines: That's fine. I've been taunted by a girl who's name is surprisingly the same as yours before.
Mabel: Really? Almost same here. Wait, then that means...
Dipper: It's pretty much the opposite here, Mabel. You were right, apparantly there is another universe that's basically has the opposite personalities.
Mabel: Wow. Well, I'm going to meet our versions!
Gideon Pines: Mabel, wait. They are more evil than me and Pacifica in your universe as it sounds like.
Dipper: Nah, I bet it's the same. Either way, I wouldn't go Mabel.
Mabel: That's water over troubled bridge. "leaves"
Dipper: I have a bad feeling about this...
Mabel: "gets to the Gleeful house"
Dipper Gleeful: "sees Mabel through the window" Wait a minute... how is that even...?
Mabel Gleeful: What are you talking about, Dipper?
Dipper Gleeful: There's a girl outside that looks like you.
Mabel Gleeful: Oh wow.
Mabel: "rings the doorbell"
Dipper Gleeful: "opens the door" Hi there.
Mabel: Hi. Oh my gosh, you look just like my brother!
Dipper Gleeful: Huh, funny, because you look like my sister.
Mabel: So, I heard you guys were a little evil.
Dipper Gleeful: You must have heard that from Pacifica and Gideon Pines. They're lying.
Mabel: Really?
Dipper Gleeful: Oh yeah. We're really not that evil. They just say that just so that they get 'popular' around here.
Stan Gleeful: "off screen" Who's at the door?
Mabel Gleeful: Oh, just a friend.
Dipper Gleeful: Hey, why don't we go to the Mystery Shack and pay Pacifica and Gideon a visit.
Mabel: Ok! Oh, along the way, you might meet my brother.
Dipper Gleeful: Oh ok, I guess.
(Dipper gets to the Gleeful house right when Mabel and Dipper & Mabel Gleeful go to the Mystery Shack)
Dipper: "knocks on the door"
Stan Gleeful: "opens the door" Dipper? What are you doing in those clothes?
Dipper: Stan?? Why do you look like Bu-oh, never mind. Uh, have you seen Mabel?
Stan Gleeful: Sure did, she and her friend were going to the Mystery Shack. I thought you went you too?
Dipper: Actually, I'm gonna head there now. Thanks Stan.
Stan Gleeful: Your welcome.
Mabel: "at the Mystery Shack" "to Mabel Gleeful" Why did you take me into the room with the carpet that switches bodies?
Mabel Gleeful: Oh just because. "purposely pushes Mabel out of the room and locks herself in"
Mabel: "she thinks she tripped" Whoops. Sorry about that!
Mabel Gleeful: Accidents happen. "takes off her shoes and rubs on the carpet to start an electric charge on herself" If you can give me the key, I'll just get out.
Mabel: Ok...i guess. "when she puts the key under the door, Mabel Gleeful touches her finger and they switch bodies" "in Mabel Gleeful's body" Ugh, what just happened? "looks in the mirror" "gasps" You tricked me!
Mabel Gleeful: "in Mabel's body" "sarcastic" Whoops.
Dipper Gleeful: "grabs the key and unlocks the door and enters the room and slides the key under the door again"
Mabel: (facepalm) You do realize you just locked ourselves in this room?
Dipper Gleeful: So?
Mabel: I think you and Mabel lied about how you're not evil. You ARE evil!
Dipper Gleeful: I'm more eviller though.
TO BE CONTINUED