
Thanks to the folks at the Gravity Falls Wiki, we have this complete image of the pieces that were flashed at the end of the shorts' credits. There are two different kinds of codes to look for, the cryptograms at the bottom of the picture and the numbers in the brackets along the top and bottom of the picture. They were originally shown in this order:
1) #76 “That Thing” (The Candy Monster):
IURP WKH ILUVW XQWLO WKH ODVW VHDUFK
[13) 8, 9, 10] [14, 17, 22
2) #32 “Grunkle Stan’s Tattoo”:
No letter cryptogram
[1) 14] [2) 5, 24 3) 3] [5) 7, 9]
3) #54 "The Mailbox"
No letter cryptogram
[6) 33, 40, 46 9) 1, 18] [10) 32, 33] [39
4) #82 (Lefty)
WKHP DOO ZHOFRPH WR JUDYLWB IDOOV
[17) 6, 12 20) 3, 4]
5) #42 "The Tooth"
FRGHV RI FUHGLWV SDVW RQH PHDQV RQH VR VHDUFK
14) 21, 30, 32 15) 13, 20] [22 16) 20]
6) #132 "The Hide-Behind"
No letter cryptogram
11) 4, 12, 18] [12) 8, 9] [17, 18]
The Caesar cipher is used to decode the letter cryptograms, and you get this:
1) FROM THE FIRST UNTIL THE LAST SEARCH THE
4) THEM ALL WELCOME TO GRAVITY FALLS
5) CODES OF CREDITS PAST ONE MEANS ONE SO SEARCH
Now put them in the order you see in the complete image and you get this:
FROM THE FIRST UNTIL THE LAST SEARCH THE CODES OF CREDITS PAST ONE MEANS ONE SO SEARCH THEM ALL WELCOME TO GRAVITY FALLS
This refers to the cryptograms shown at the end of the previous full-length episodes. And this is where the numbers in the brackets come into play. Each set inside the brackets are an individual word, and the number behind the end parentheses refers to the episode number of the cryptogram to be used. Here's what I mean:
From the first short: [13) 8, 9, 10] [14, 17, 22
The number behind the first end parenthesis, 13, refers to episode 13, "Boss Mabel". The numbers that follow correlate to the cryptogram at the end of the credits: "HEAVY IS THE HEAD THAT WEARS THE FEZ"
Now, "ONE MEANS ONE" as the shorts' cryptogram says. So, count from the first letter of Boss Mabel's cryptogram:
8 = T, 9 = H, 10 = E
and
14 = D, 17 = A, 22 = R
The other thing to notice about this particular set of numbers is that 8, 9, and 10 are in one set of brackets while 14, 17, and 22 are in another - and not a complete set. We need the complete image to put together the bracket sets in order. Here's what we come up with:
[1) 14] [2) 5, 24 3) 3] [5) 7, 9] [6) 33, 40, 46 9) 1, 18] [10) 32, 33] [39 11) 4, 12, 18] [12) 8, 9] [17, 18] [13) 8, 9, 10] [14, 17, 22 14) 21, 30, 32 15) 13, 20] [22 16) 20] [17) 6, 12 20) 3, 4]
As noted above, sometimes a set of numbers inside a set of brackets is made up of groupings from multiple episodes, and can begin with numbers from an episode mentioned in the bracket before.
Now that the complete list has been assembled, here are the numbers decoded:
[I] [WAS] [SO] [BLIND] [HE] [LIED] [TO] [ME] [THE] [DARKNESS] [IS] [NEAR]
Interesting, yes? And considering the assembled images form a crossed-out eye, and that the last cryptogram from "Gideon Rises" said SEARCH FOR THE BLINDEYE...
Now the questions are these (a partial list, surely): Who was blind? Was it the author of Journal #3? Who lied to this person? Was it Bill Cipher? (considering the crossed-out eye it might be worth it to lean in that direction) What will the darkness bring?
And most importantly: Are we all going to be able to last until the second season when we'll hopefully start to get the answers?