SPOILERS for Gravity Falls' season 2 & series finale (Seriously, GF is best gone into blind!). Set during MLP:FIM Season 6 after "The Crystalling". You have been warned!
This cover art is not mine. It's a placeholder until I can make my own. Found it through google. It belongs to Pony Stark. Go check out their other artwork too.
One year after Weirdmageddon, the Pines reunite in Gravity Falls for another summer of adventure. A fall into Equestria wasn't what they had in mind though, or being turned into colorful ponies...
Twilight and friends seek to help the lost travelers return home, but meanwhile, a new danger sets its sights on Equestria, and revenge.
MLP / Gravity Falls Crossover
Big Thanks to MyOwnNameWasTaken for being my Beta Reader. Go check out his stories, too! 
Author's Note: So after the epic Gravity Falls finale that was Weirdmageddon, and the welcome surprise of MLP's season 6 starting, I got inspired to write this. Hope you like it! Also, to those wondering about Daring Do and the Order of the Eagle, yes, I do plan on continuing it and fixing those first chapters. But I currently have writer's block for it, unfortunately, as well as other projects, so that might take a little while. 
P.S. To those readers who feel the need to give me "thumbs down" votes: I would really appreciate it if you would please leave a comment telling me why you down-voted. I can't improve my writing if I don't know what I'm doing wrong. Thank you.
Obligatory Disclaimer: I do not own Gravity Falls or My Little Pony: Friendship is Magic. Gravity Falls is owned by Disney. Everybody here already knows who MLP is owned by.
Is Bill Cipher the main villain?
7099646
That would be spoiling, now wouldn't it?
Eeyup!
Well, this should be interesting, I'm a big Gravity Falls fan as well as MLP, so I'm curious to see where this goes.
That deleted scene. WHY COULDN'T YOU FINISH IT AND PUT IT IN?! Anyway this is awesome.
When is the next update. This is awesome. Keep up the great work.
Is this a sequel?
7150996
A sequel to what?
7113226
It just got updated. :)
Nice chapter, I'm curious to see where this goes
.
I would really like to see ford's reaction to Luna in his dream, it would probably go like this:
Luna: hello, subject, we are here to contact you through your dreams to ask yo-
Ford: DREAM DEAMON! Are you friends with Bill? Do you want me to help you get him back? I WILL NOT MAKE ANY DEALS WITH YOU!
Luna: what is a dream deamon? And who is the 'Bill' you speak of?
UPDATE SOON FOR THE PINES,
and for bill
(LAUGHS EVILY)
7113173 I agree.
7154985 Yep, that reaction would be hilarious.
A gravity falls crossover? Well I'll definitely track this!
For as good as this story is it has a surprising lack of up votes.
7290415
That's probably because I made the mistake of uploading chapters 1-4 all at once...
I'm normally not a fan of crossovers, but this was just great. Good job!
Awesome chapter
I am still waiting on that first paranoia-induced reaction from Vwdqirug
Are those actual ciphers you use to replace their names? or is it just gibberish? I thought it was a clever reference to one of the themes of Gravity Falls, but i could be wrong.
7301754
It's an actual cipher.
See my Author's Note at the end of the chapter if you want to solve it. 
They said princess moon. Button for once!
Can you countinhe soon
Ive heard of geetibg stronger[youtube=]
They said princess moon. Button for once!
Can you countinhe soon
Ive heard of geetibg stronger[youtube=] http://www.google.com/url?q=https://www.youtube.com/watch%253Fv%253DGDpmVUEjagg&sa=U&ved=0ahUKEwjBw7vz9eHNAhUFOSYKHZn9DnIQtwIIEzAB&usg=AFQjCNGZLSa_Q6gX37CZWnIoDGJ0ESR9tQ
7290415 The right people haven't found it yet.
Slightly saddened by using "Muffins" instead of Derpy or Ditzy, but other than that, fantastic crossover!
Curious to see where this goes. You've got all of the character voices down perfectly.
Wow, I just noticed one of my stories is in the "Also Liked" Column. Neat!
Also, can't wait for the next update!
I'm very confused as to how you got this mess approved by Equestria Daily.
Well just caught up and so far a bit darker than I expected for this kind of crossover at the moment, it's still a good one. Although it does seem to have taken a long time for them to meet up at least in part I hope they stick around a bit since they obviously have to deal with the remnants of Cipher.
Although one problem, can Luna even enter Ford's mind? Remember that Ford had that metal plate installed and has done who knows what to keep his mind closed off to anyone that tries to enter it. I'm not sure Luna could enter his mind unless Ford allows it. In fact I really hope the next part is her trying and surprised to find out his mind is shielded and tries to get the others help to give a message since at least two people dreaming of a blue pony princess can't be put off as just a dream.
7479608
Don't worry, it will get lighter once they get out of the forest and start interacting with Ponyville.
From what we learned in "The Last Mabelcorn" and "Weirdmageddon", Luna should be perfectly capable of entering Ford's dreams, As Ford says to Bill, "You can haunt my dreams, but you can't enter my mind unless I shake your hand and let you in." So I think it's only his awake, conscious mind that the metal plate shields.
7479379 Well, what exactly confuses you?
Well, this should be interesting...
Really? I'm quite enjoying it. I was always a bigger fan of Gravity Falls than MLP, and this chapter alone gave me such feelings that I temporarily forgot that it is a fan fiction.
7431943
Sadly, at one point they made "Muffins" her canon name.
The splinting scene was quite touching.
Thank you very much for writing this story. More please!
7480569 She's Muffins on the end credits of "Slice of Life", however, her name is never said on screen and even the crew of the show call her "Derpy. "Muffins" is more of a placeholder than anything else since Hasbro won't let the crew use her name.
AMAZING!!!! You have inspired me to write my own stories
7479633 Oh one question I had, is Bill's return going to be explained as because Stan started to get his memories back that he was able to return or will Bill's last spell he said as he was defeated going to play into this story? Just asking since he said "A-X-O-L-O-T-L, My time has come to burn, I invoke the ancient power that I may return."
Okay he said it backwards and I didn't know he said that until someone posted youtube videos of the audio reversed but I was just wondering if that would play into this.
7483599 I'm still thinking that over... You guys will know when I do though. :)
7480542 agreed
Noice
I called it on Stanford thinking she would be a dream demon!
and don't forget: FIRST!
Thanks for the update!
So now that is out of the way I take it the next chapter will be the morning and seeing what happened to Mable with the poison joke she ate. Although if they are this deep into the forest it's not going to be easy getting back to that hole once they're done here since it looks to be like a 2 day travel time on land to get there. Well a problem for another time since the castle is pretty close to Ponyville (since they seem to travel there within the day easily enough in the show). I hope the name thing is just for the minds and this won't show up when they are awake in their pony forms.
Honestly I'm not sure why you would bother with that as everything else is in English and should be understandable anyway.
7494980 Well my thinking was that if this had been a "wizard-made" portal, like the Equestria Girls mirror, then they would be able to speak each other's languages. But since this is a "wild" portal, the language barrier is still there.
7494762 that's what i thought about that when i saw his reaction "wow, he actually nailed it with the reaction!" lol
BTW: SECOND!
7495137 Wait that doesn't mean that they won't understand each other when they meet up will it? Because I really hope not as that seems a bit of a unnecessary complication put into this kind of crossover at the moment.
7495340
I see your point, but here's the thing. Most people, when they say a noun or a verb, have an object or concept in mind. It could be argued that magic is crossing the language barrier by translating not the words, but the concepts. However, most people are unaware of any meaning behind the word that is their name; to them, it's just the collection of syllables that differentiates them from others. I could see how magic might be unable to translate something that, even to the speaker, is nothing but a collection of sounds.
Diplomacy at work.