I organized it more or less by relevance (under the cut because this is a long post). If you haven’t already, you can read the AMA for yourself here.
Silly stuff:
Dipper’s internet history has lots of pictures of redheads
according to Bill, the guy on the other side of the magical mailbox is “a real blabbermouth”
Time Baby is the last son of an extinct race of time giants
men have nipples because humans were designed by “a blind and uncaring chaos”
Bill thinks in all caps
dream catchers tickled Bill
Bill has done banking with Thomas J Beale
Operation Northwoods is the worst that could happen
love is our “sick raw biological urge to reproduce trying to dress up in a suit and charm its way through the opera”
Bill hates kryptos
Bill likes to people watch in Gravity Falls from “the skulls of the gullible”
Bill plants predictive programming of false flag attacks in media as a hobby
the meaning of life for mortals is procreation
the AMA took place at such a random time to test our faith
Bill’s favorite constellation is the solar system of Teegeeack (the name of Earth in scientology)
Wendy is a pushover
Bill’s dimensions has 14 billion different genders
More relevant information:
according to Bill, big things are coming
Bill hates Time Baby with a burning passion
there are demons other than Bill
Bill has been around since at least before the pyramids
Bill can see infinite possible futures, as well as infinite alternate universes
when asked who we should beware of, Bill replied with a link to The Blob theme song
Bill’s powers have limits
Edwin Abbott Abbott had a decent idea as to what spawned Bill’s existence
according to Bill, Stanley has made enough mistakes without Bill’s help
Bill exists in a state of quantum uncertainty, like Schrodinger’s cat
every image of Bill serves as a peephole from his dimension to ours
Bill knows Dipper’s true name
Bill Cipher isn’t Bill’s actual name - if we heard his actual name we’d evaporate
Stan’s tattoo means “watch your step”
Bill used to have family, but no longer does
Bill “likes Gompers better this way”
the character Tad Strange is “a real square”, according to Bill
Other noteworthy comments:
“WELL IT LOOKS LIKE THE KIDS REM CYCLE IS ABOUT TO END, SO I SHOULD MAKE LIKE A PINE TREE AND BURN TO THE GROUND!”
this could tie into the burning tree shown on the tapestry
“I HAVE EYES IN MANY PLACES. I HAVE FRIENDS WITH MANY FACES. I KEEP THE PINES IN PROPER PLACES. DONT LOOK NOW - I UNTIED YOUR LACES”
(referring to the tapestry) “IT CAME OUT PRETTY NICE, DONT YOU THINK?! THE NATIVE PEOPLE OF GRAVITY FALLS REALLY HAD A FLARE FOR CAPTURING MY TRUE ESSENCE. ALTHOUGH THEIR TIMING ON PROPHECIES LEFT SOMETHING TO BE DESIRED! GOTTA HAND IT TO THAT SHAMAN THOUGH, HE WAS A REAL FUN GUY TO TALK TO, EVEN IF HE TURNED OUT TO BE LESS COOPERATIVE THAN I HOPED. HEY, THERE'S ALWAYS THE NEXT GENERATION...”
the tapestry is implied to have been created by the native people of Gravity Falls, as well as inspired by a prophecy
maybe they thought the prophecy would come true in their time, but their timing was off and it’s now coming true in Dipper & Mabel’s time?
the mention of the next generation could mean that there will be a character similar to a shaman that appears
“LIE UNTIL WHAT YOU WANT TO BE TRUE BECOMES TRUE. LIE UNTIL YOU CANT REMEMBER WHAT’S A LIE AND WHAT ISNT. LIE UNTIL YOU ARENT LYING ANYMORE.”
Bill could be alluding to a specific person in Gravity Falls (personally, I think it’s Grunkle Stan, because he’s definitely had practicing with lying and pretending to be someone else)
one person asked if Bill had any sort of “back door” into Dipper’s mind after possessing him, saying that in their religion, people aren’t free from demons until after being blessed or purified, Bill just responded with “ALL RELIGIONS ARE WRONG! PLEASANT DREAMS!”
“ALRIGHT, YOU GOT ME, I MIGHT HAVE OVERSTUFFED MY RESUME! HEY, THEY SAY DRESS FOR THE JOB YOU WANT, NOT THE ONE YOU HAVE! BUT JUST BECAUSE MY POWER HAS A FEW BLIND SPOTS NOW DOESN'T MEAN I'M NOT ANGLING FOR A PROMOTION, YOU DIG?”
(this was how Bill explained he wasn’t really all-powerful) the mention of a resume and a promotion could imply that there are demons more powerful than Bill and/or some sort of demon hierarchy
when asked if we would see Bill after the end of the 2nd season, Bill responded with a link to the opening of the show Eerie Indiana
the show Eerie Indiana had only 2 seasons, and the 2nd season was a version of the same town as the 1st season, but in an alternate dimension, with completely different actors
Bill could be implying that we won’t see him after season 2 or in the 2nd half of season two because he’ll be an alternate dimension
he could also be implying that the entire town of Gravity Falls will shift into another dimension due to the portal/apocalypse
when asked “What do you think about Stan Pine’s brother?” Bill responded with “WHICH ONE?”
this could be interpreted 2 ways:
1. Grunkle Stan has a second brother
2. “Stan Pines” can refer to Stanford or Stanley, so “Stan Pine’s brother” could refer to Stanford (Stanley’s brother) or Stanley (Stanford’s brother), so there isn’t actually a third Pines brother