This is my ideal episode for Gravity Falls, A Gravity Falls/Phineas and Ferb Crossover!
(scene shows Dipper and Mabel in their room, Mabel just laying on the bed while Dipper is reading the book)
Mabel: I'm bored. I wish something exciting with danger and mayhem happens!
Dipper: (looks at a word in the book) Hmm, I wonder what this word means.
Mabel: What do you mean?
(as he says this word, a portal opens up)
Mabel: Whoa! I wonder where this leads!
Dipper: Better let me go in first. (he puts down the book and enters portal)
(Dipper is shown in the backyard of Phineas and Ferb)
Mabel: Cool. (looks in window door) Hey look, we're more-ly animated.
Dipper: I wonder where we are? (he leans into the tree and presses a button and slips into the tree)
Mabel: Dipper! (follows Dipper)
(meanwhile, Phineas and Ferb wake up and walk into the backyard when they see the portal)
Phineas: Whoa, a portal. Cool!
Isabella: Hey Phineas. Watcha doin'?
Phineas: We've discovered a portal!
Isabella: Wow! We should go in!
(they go into the portal and are in Mabel's and Dipper's room)
Isabella: Whoa, where are we?
Phineas: (picks up the book) I'm not sure, but look at this book. (looks through book) Wow, look at all this! Ferb, I know what we're gonna do today! We're gonna have an adventure!
(theme plays (the theme is similar to Jimmy Timmy Power Hour; the way that 2 theme songs play at the same time))
(Mabel and Dipper enter Perry's lair)
Dipper: Where are we?
Mabel: Cool, a jet pack!
Major Monogram: (appears on the screen) Morning, Agen-Great googly moogly! Carl, who are these kids?
Carl: (off screen) They must be Agent P's owner's friends.
Dipper: Um, what's the mission?
Major Monogram: Um, I guess I'll just give you the briefing. Doofenshmirtz has been seen in town and going through a strange portal. You need to go to Doofenshmirtz Evil Incorparated and find out what he's been up to.
Dipper: Thanks. Come on, Mabel. (they get on the hover car)
Phineas: Wow, check this out guys. Gnomes, manotaurs, and ghosts! I wonder what we should do first. (they head downstairs when they see Wendy and Soos)
Soos: Hey, where's Mabel and Dipper?
Phineas: Who's Mabel and Dipper?
Wendy: They are 2 kids that live here.
Phineas: They must have made that portal that lead to our backyard. But how did they do that?
Doofenshmirtz Evil Incorperated!
Dipper: Well, this is the place. (enters room and is heard screaming)
Mabel: Dipper! (enters room and sees Dipper in a trap)
Doofenshmirtz: Ah-oh, sorry about that. I wasn't trying to trap you, I was gonna trap someone else. But, now that you're here, I guess I should tell my latest invention! Behold, the Mute-inator!
Mabel: The what-inator?
Doof: The Mute-inator. It makes everyone that it zaps speechless.
Dipper: (gets free of trap) Who are you again?
Doof: I'm Heinz Doofenshmirtz.
Dipper: Doofenshmirtz? That name sounds familier. I won-(sees that the book isn't in backpack) Hey, where's the book?
Mabel: I think you left it in the room.
Dipper: Oh, darn it!
(at the Flynn-Fletcher house)
Linda: Candace, I'm gonna go to the grocery store to get some things. Until I come back, you're in charge.
Candace: Ok, mom. (goes outside to the backyard) Mom sa-Hey, where are they? (sees portal) Ugh! Phineas! Ferb! Come out now! Ugh, if you don't come out, then I'll take you out on my own! (enters portal)
Dipper: I guess we'll head back.
Doof: Ok, nice seeing you!
(as they are about to leave, Perry enters the room)
Mabel: I think that's Agent P.
Dipper: Uh, let's just go.
Doof: "when they leave" Ah, Perry the platypus! Who were they? Oh, I don't know. Well, I was gonna fire up a new invention called the Mute-inator, but then I decided, since I haven't really shot it yet, why don't I fire up the Forget-about-it-inator!
Phineas: I can't wait when we have a real adventure in this book! (sees Candace) Oh, hey Candace!
Candace: What are you guys up too and where are we?
Phineas: Well, according to Soos and Wendy, we are in Gravity Falls.
Candace: Who are they?
Phineas: Two people we just met.
Candace: Whatever, I'm taking you 2 to home now.
Phineas: Ok. (he leaves the book on the counter near Soos)
Dipper: Well, here we are again.
Mabel: I think I remember that word now! It's Ztrimhsnefood. (when she says this, the portal closes) Whoops.
Doof: (it shows Perry stuck in glue and sand paper) Ah ha! Now you are stuck! At last, I am finally gonna fire it up! (fires the inator)
Dipper: Don't worry Mabel, It's... (him and Mabel get hit by inator) ...what was I talking about?
Mabel: I don't know.
Dipper: Uh, Mabel. I think we lost the password back to Gravity Falls! Now we're stuck here!
Candace: I know the portal was around here somewhere!
Isabella: Maybe it dissappeared!
Phineas: If it dissappeared, that means we're stuck here!
Isabella & Candace: "gasps"
TO BE CONTINUED IN THE NEXT PART