Also in the Japanese dub, Farmworld Finn has a metal right arm with the ability to turn into a blade. That sounds just like a certain character that Romi Park used to voice who also has long blond hair.
Also from "Lady & Peebles", Ricardio says this line:
"Ohhh, myyy "
In "Memories of Boom-Boom Mountain", the Head Marauder (played by Tom Wilson) calls Finn a chicken, and Finn angrily responds "What did you call me?"
In "Candy Streets", Pete plays another Pete in the Disney line up.
Dana Snyder plays a wizard whose magic grants life to inanimate objects which then go on to terrorize others. Believe it or not, that's a regular motif on Aqua Teen Hunger Force.
"Everything Jake" features Billy West as a guest actor, voicing numerous characters found inside Jake's mind and body. The first friend who sees Jake sounds almost like Fry, but not quite. They comment on how it's been a few years since they last saw each other (the end of the production of Futurama). He uses his actual Zapp Brannigan, Tinny Tim, and Professor Farnsworth voices on other characters.
The character with Farnsworth's voice has a father who is, by all appearances, much younger than he is. This echos Farnsworth's relationship with his Great-uncle Fry.
In Evergreen, the Candy Elemental Chatsberry is voiced by Alan Tudyk, AKA King Candy.
Adored by the Network: The show was this back in the day. It was very much adored along with Regular Show and, to a lesser extent, The Amazing World of Gumball. It would eventually be surpassed by the latter of the three as the network's favorite, and would eventually be dethroned completely by Teen Titans Go!, to the point that, as of October 2015, zero Adventure Time re-runs are on the schedule, meaning the only places the series can be watched are video on-demand, on the official Cartoon Network app, on the DVD and Blu-Ray releases, and on YouTube (if the copyright police haven't taken down the episodes yet). Fortunately, re-runs finally returned on October 25, 2015 in the lead-up to the seventh season. It used to air on Saturday evenings as part of a block called Regular Time Adventure Show (which features new episodes and reruns of Adventure Time and Regular Show) on March 5, 2016, but now, as of May 5, 2016, has moved back to Thursdays.
In spite of getting Screwed by the Network for the final years of its' run, Cartoon Network aired a marathon of fan favorite episodes on September 3, 2018 leading up to the series finale. Then, they proceeded to air reruns of the show, as well as said special, every day after its' premiere. This surprised many fans, as Cartoon Network usually only gives this treatment to special episodes of Teen Titans Go!.
One fan made a drawing of a tiny cat assassin named Me-Mow. The creators liked the idea, and thus, the episode "Jake vs. Me-Mow" was born.
Sort of. Liz Prince wrote a 7-page story called "Fruit Salad Days" for Marceline and the Scream Queens Issue 3, in which Lemongrab was the frontman of a punk rock band called "Unacceptable." Liz Prince's idea of Lemongrab having a punk band named Unacceptable was actually re-used for an official Adventure Time game and comics the following year.
Finn's 13th birthday episode first aired, coincidentally, on Pi Day (March 14, 2011) which first Fanon and later Word of God made his birthday.
The Cartoon Network Australia version of Adventure Time has a truckload of stuff cut out due to censorship, making a lot of episodes look and sound choppy and incomprehensible...
Cartoon Network Latin America censored some chapters, too. Even worse, some chapters are banned from the channel.
The UK DVD issues have no special features. The British Season Two DVD had four full episodes missing, including some highly significant ones for larger arcs, and the Season Three DVD leaves out another four.
Banned Episode: The first printing of the eleventh issue of the ongoing comic was pulled from stores at the last minute and pulped - not because of any content in the story itself, but because a house ad for Bravest Warriors showed a character making what was considered to be an all-ages-inappropriate hand gesture.
Banned in China: In Australia, episodes that aren't butchered are merely pulled from rotation (such as "Fionna and Cake" and "What Was Missing" due to many scenes deemed too sexually suggestive). Thankfully, when the series appeared on free-to-air it was screened unedited (though a few episodes were out of order).
The episodes "Wake Up", "Escape from the Citadel", "The Tower" and "Breezy" were banned in several countries (including the United Kingdom and Poland), creating several plot holes.
Also, the episode "All the Little People" was banned by Cartoon Network in Latin America due to its content. Furthermore, the episode isn't available legally on Netflix. However, the chapter was broadcasted uncensored in FTA channels.
The series itself got banned in Kenya in 2017 for its homosexual themes along with a number of other children's shows, as same-sex sexual relations are illegal in that country.
In "The Limit" Jake says he can't blink... and then blinks mere seconds later.
They forgot to put the snail in "Trouble in Lumpy Space" and "Blood under the Skin".
In "Business Time", they misspell Finn's name as "Fin".
In "Reign of Gunthers", Princess Bubblegum says "calvary" instead of "cavalry" at one point, which is more out of character than Finn's malapropism above.
In "You Made Me!", Lemongrab's shoes randomly disappear when he takes out the Sound Sword for the first time.
Cash Cow Franchise: On top of the things listed on the franchise page, it also has various toy and clothing merchandises with more still to come. Even though the show itself doesn't air as often as it used to, it's still having merchandise churned out.
Olivia Olson as Marceline displays her vocal skills in multiple episodes.
The Gender Bending episodes seem built around the idea of having the guest cast sing. Madeline Martin voices Fionna the Human and sings in both episodes, with NPH-as-Prince Gumball in "Adventure Time with Fionna and Cake" then Donald Glover who voices Marshall Lee, sharing a duet and singing to Fionna in "Bad Little Boy".
Jake gets to show off John Dimaggio's beatboxing skills at the beginning of "Conquest Of Cuteness."
Creator Breakdown: Pen Ward quit as the showrunner during season 5 as he couldn't handle the influx of work and stress which came with running an extremely successful show. He now only serves as creative input and the voice of Lumpy Space Princess.
Creator Cameo: In "The Hard Easy", Woobeewoo is voiced by Kent Osborne, one of the show's writers and storyboard artists. He also plays Joshua, Jake's and Finn's dad.
In "Storytelling" and "Jake the Dad" the fox is played by Tom Herpich, another of the show writers and storyboard artists. He also co-wrote those episodes.
Cole Sanchez voices the Party God.
Root Beer Guy is voiced by Jack Pendarvis, one of the writers.
In "Billy's Bucket List," Canyon is voiced by Ako Castuera who co-wrote the episode.
Steve Wolfhard voices Slimey D and the Ice Imp in "Evergreen."
Pendleton Ward himself voices many characters in the series, including main character Lumpy Space Princess.
According to Ghostshrimp in his podcast, the production crew was expecting Cartoon Network to renew the series for another season while they were still working on Season 9, but the channel cancelled the series mid-production, leaving only four episodes for the crew to work with. These four episodes became the series finale.
God Never Said That: Andy Ristaino (character designer) never said that "What Was Missing" was a musical. He said that the episode would kind of resemble one because it has a couple of songs in it.
This was the reason for the whole "BubblegumXMarceline Mathematical" fiasco. Frederator took down the video because it made it seem like the show was openly asking for plot input for further PBxMarcy development and Adam Muto, the storyboard artist and writer of the episode, didn't like the video framing that interpretation as only being romantic.
God Does Not Own This World: Pen Ward may be the main creative force behind Adventure Time, but if we wanna get really technical, Cartoon Network owns the show, not him (though that should be kind of obvious). From an interview:
Pen: I get a lot of emails from people asking, "Can you give me permission to make this?" Well, first of all, I don't own Adventure Time, so I couldn't give permission if I wanted to.
If neither of those possibilities are correct, it qualifies as one of the most amazing coincidences ever.
According to the NASA article, it's an old photographer's trick. They put an item they know the size of in the photographs for scale.
"Hot Diggity Doom": The King of Ooo, a popular figure with amazing hair, expensive taste, and dubious personal style uses populist rhetoric to get elected over his somewhat out-of-touch (and not exactly squeaky clean) female opponent who is so shocked at being beaten she goes into isolation for months.
Played straight with Zack Shada. Zack hit puberty and he couldn't get his voice to sound like Finn's anymore, so when the show went from being a Nickelodeon pilot to a Cartoon Network series, the voice director got Jeremy Shada (Zack's younger brother). Now averted with Jeremy, as rather than get rid of him because of his voice changing, the writers incorporated Jeremy's vocal change to Finn's by periodically aging him (by the series finale, he's 17).
Princess Bubblegum is played by Paige Moss in the pilot and Hynden Walch in the series.
In the pilot, Lady Rainicorn was voiced by Dee Bradley Baker and spoke nonsense. In the show, her voice actress is Niki Yang (the same Niki Yang who plays BMO) and the nonsense was replaced with fluent Korean.
Tiffany was voiced by Vincenzo Rauzo in his first appearance in "My Two Favorite People". He has been voiced by Collin Dean in the character's subsequent appearences.
Ghost Princess is played by Pen in "Loyalty to the King" and Maria Bamford in "Ghost Princess".
In the video game, Marceline is played by Jessie Seely instead of Olivia Olson. Granted, the difference is barely noticeable.
In "Davey", to make his disguise more authentic, Finn changes his vocal chords to a more adult tone of Davey Johnson.
In his first appearance, the Cosmic Owl has a feminine-sounding voice provided by Finn's actor, Jeremy Shada. In his next speaking role, M. Emmet Walsh took over the role and gave him a much more masculine, older-sounding voice.
John DiMaggio voiced Jake's brother Jermaine in "Crystals Have Power", but in "Jermaine" he's voiced by Tom Scharpling of Steven Universe.
Huntress Wizard is voiced by Maria Bamford in "Reign of Gunters", but in "Flute Spell", she's voiced by Jenny Slate, fresh out of Zootopia.
Felicia Day replaced Lena Dunham as Betty for the Elements mini-series.
Permanent Placeholder: The main title theme was a scratch recording. Originally played and sung by Pendleton Ward, in the background you can hear storyboard artist Derek Drymon typing on a keyboard and squeaking his chair. Ward attempted to get a better recording of the theme song but couldn't ever capture the feeling quite right ever again, so the scratch recording stayed.
Playing with Character Type: At first, the Ice King seems no different than Tom Kenny's usual characters, until the Christmas Episode "Holly Jolly Secrets" where it's revealed that The Ice King was once a man named Simon Petrikov and that he became the Ice King after wearing a crown that drove him to insanity.
Production Nickname: The staff have mentioned◊ jokingly calling the shape-shifter from "Joshua and Margaret Investigates" who turns out to be Jake's biological parent "The Peeper".
Schedule Slip: Season 8 was originally planned to premiere in 2016 alongside the "Islands" miniseries. However, according to an interview with Adam Muto, Season 8 was delayed to early 2017 after the series was announced to end in 2018, in order for the crew to take their time to work on the final season. This decision also delayed the final episodes of Season 7, "Preboot" and "Reboot", to November 2016.
Screwed by the Network: In 2015, the series began getting this treatment for unknown reasons, though the saturation of the schedule with Teen Titans Go! reruns (either for financial reasons, or so the network can artificially lower the series' ratings to justify shitcanning it), its age (the series premiered in 2010, and is pretty old by industry standards), or Moral Guardians (the show has had alot of violence, some gore, and many Getting Crap Past the Radar moments) are most likely to blame. The series wasn't rerun much in 2015, and new episodes are only advertised online. The situation slightly improved in mid-2016 with better advertising, but reruns were still non-existent, meaning if one missed an episode, they would have to watch online (either through the CN app, on unofficial hosting sites, or outright piracy), or through video on-demand services.
The screwing intensified in mid-late 2016. In September, it was announced the series would end after its ninth season in 2018. Then, the Finn & Jake balloon did not show up in the line-up for the 2016 Macy's Thanksgiving Day Parade, meaning it was retired. And finally, the two-part seventh season finale aired in other countries before the United States, received zero promotion in the US, and was suddently rescheduled right before its airing, giving it the series' lowest ratings. This treatment of Invisible Advertising continued for Seasons 8 and 9, and a complete lack of reruns (aside from the "Stakes" miniseries airing on the weekend before Halloween due to being thematically appropriate; a regular rerun schedule wasn't re-established until June 2017, when the series began airing in an hour-long block on Mondays at noon) makes it very clear that Cartoon Network is working as hard as it can to snuff out what was once its flagship series.
The production team had actually planned for a tenth season, only to be informed that while they were working on the ninth, the network had chosen not to renew it. So season nine had to be reworked to give it an ending.
Shrug of God: Whenever someone is asked whether Susan is human or not. The answer is usually "Come up with your own conclusion." "Deep Purple" eventually revealed that she's a human with some cyborg augmentation.
The same answer is usually given regarding the relationship between Lemongrab and his clone. Princess Bubblegum and Marceline used to get a lot of this to until Olivia Olson finally just flat out confirmed that they're ex-girlfriends. They can never explicitly say it in the series, though, because the series airs in countries where homosexuality is illegal (IE Russia). Ornot.
Spoiler: Though the spoilers don't actually happen "in-show". A lot of the season one storyboards could be viewed online before their episodes even aired. But hey, it would be fun to watch the episodes to see if anything got changed.
Pen Ward blatantly mentioned at Comic-con that Flame Princess would be Finn's new love interest before "Incendium" aired. However, he didn't spoil her destructive personality and only called her "intense" (a word that a member of the audience laughed at).
TV Guide spoiled the fact that the short stories in "Five Short Graybles" are centered around the five senses (sight, touch, taste, smell, and hearing). It wasn't supposed to be revealed until the end of the episode. It really makes "Huh? You still haven't figured it out?" less funny.
An ad from Gamestop Canada showed some scenes from "The Comet" before the episode aired on North America.
The DVD cover for "Islands" was posted online weeks before Cartoon Network posted the opening on their social media accounts. Said cover also revealed Finn's robotic arm.
A short clip from "Always BMO Closing" was shown in a bumper three months before the premiere of Season 9. Said clip also revealed that Jake returned to his original self, since the last thing AT related CN aired at the time was the "Elements" miniseries.
Cartoon Network itself spoiled the ending of "The Wild Hunt" on Facebook and Twitter hours before the premiere of Season 9, revealing Uncle Gumbald's identity and Fern's new Green Knight look.
While it's not clear if any of her characters talked to each other, stand-up comedian Maria Bamford has voiced twenty-six voices for the show, even doing male voices such as Manfried in "Slumber Party Panic" and the Butterfly Bandit in "The Other Tarts".
Justin Roiland voices Lemongrab, Lemongrab's clone, and all of their children.
Teasing Creator: A lot, if not most, of the staff count. Exhibit A, Adam Muto:
The staff loves to remind the fans that Fionna and Cake and related characters will never be part of the main AT universe. Hasn't stopped fanfiction writers, though.
Throw It In!: An unusual example. When Adam Muto originally pitched "What Was Missing", he flubbed the original line that read "I'll get your toy back, kid!", and he said "I'll get your kid back, toy!". They thought it was funny that way, so they kept the line flubbed.
In "Goliad", the titular character (voiced by writer GrahamLinehan's daughter) badly flubs the line "I'm Don Juan Cherry Tempo!" but the producers clearly thought it was so adorable and funny that they left it in.
A lot of the fandom sees the show's writers as this. For example "Fionna and Cake" basically compares the Ice King to fanfic writers. Many fans see "All the Little People" as a Take That! and parody of shippers in general. And then there's the end of "Mystery Dungeon" where Ice King didn't get to make the Fionna and Cake world real, which is what many fans wanted. In particular, many fans advocate a meeting between Finn and Fionna, to the point that the Finn/Fionna ship is rather popular, though many other fans reject the ship for basically being what is referred to as "selfcest". Still others Take a Third Option and make Finn and Fionna long-lost twins.
Seeing as some fans ship the two Lemongrabs together, "Another Five Short Graybles" has the original Lemongrab eat the other, as well as revealing that they view each other as brothers rather than lovers.
Voices in One Room: The cast records their dialogue together in one room, which is rare for an animated show.
Western Zodiac: Fitting enough that Finn's element is water. His birthday, March 14th, exists in the Pisces period during the year, and Pisces' Zodiac element is water.
The original storyboard for "The Duke" has Jake imagining how evil the Duke can be. The Dramatization includes a particularly impressive Hurricane of Nut-Puns by the Duke, which includes "CASHEW LATER, COPPERS!" and "CHESTNUT YOUR DAY, JAKE!". However, this was scrapped for time.
The Princess Plant was originally supposed to be called the Halo Lily.
As mentioned before, the fact the series was originally to be on Nickelodeon.
The original ending of "Sons of Mars" would have shown Death transporting Lincoln back to Ford's Theater before fading to black with the sound of the gunshot from John Wilkes Booth. The final version has a gunshot, but no Ford's Theater, implying but not making explicit the events shown in the storyboard.
There were also several changes to "The Lich". For one, Prismo is called "The Almighty Grob", but more importantly the Lich would've been possessing Billy instead of having killed and replaced him, and Booko would have revealed that Finn's human dad was a hero who was wrongfully imprisoned in an impossible-to-escape dimension—with the implication that Billy put him there—and is still fighting the other inmates. This ties into several examples of The Artifact. In the actual series, "Grob" refers to a powerful (but not all-powerful) magical being from Mars (full name Grob Gob Glob Grod). This storyboard also reveals that Finn never realized that he was adopted (with a Lampshade Hanging on the ridiculous levels of Idiot Hero that would come along with this notion), which is obviously not the case in the series. Sadly this meant one of the series biggest heartwarming moments ended up being cut as well.
According to Jesse Moynihan, Lemongrab was not originally a socially awkward, dysfunctional, brain-damaged, unadjusted Jerkass Woobie in the original outline. He was originally conceived by Pen to be a one-shot, one-dimensional Jerkass "like Xergiok." However, Jesse stepped in, and decided to give Lemongrab the puzzling amount of depth he has, by making him "weird, isolated, angry, off-putting, with an inability to read social cues." Part of Lemongrab's appeal appears to be his many woobie-ish and sympathetic traits. If Jesse hadn't fleshed out Lemongrab's character, LG wouldn't have the zealous fanbase he has, and he probably wouldn't have been considered to make a return in the series after his exit from "Too Young".
The episode "Betty" was supposed to be a double episode, but there was already a double episode in production and Huntress Wizard appeared in a 30 second scene but it was cut for unknown reasons, possibly time reasons.
Toronto was going to appear in Apple Wedding, where he catches Princess Bubblegum rooting around in the King of Ooo's things, and she throws him in a suitcase to keep him from interfering in her investigation. He makes his debut in Gold Stars, where he's a lot more sinister.
At the end of "Hot to the Touch", Finn and Flame Princess were supposed to kiss instead of hug, but this was saved for "Burning Low". It's perhaps this reason that the latter episode is the highest-viewed episode in the series.
According to Kent Pendarvis and Ghostshrimp, if the series were to be renewed for a Season 10, there would be some episodes focused on Susan Strong, Minerva and Sweet P, as well as giving more development for Gumbald.
The four parter series finale was originally a four parter season finale with a completely different plot: it would focus on Finn meeting Gumbald and some weird people. The events of this finale would lead to a Season 10, hasn't the series been cancelled by CN.
The uproar that happened over the Ship Teasing in "What Was Missing" caused "Mathematical!" to stop producing recaps.
Nat and Pen used to make themselves known on /co/, but they stopped due to... obvious reasons. Nat later came back for the show's second anniversary. She also came back the Sunday night before the season 4 finale.
Lead character designer Andy Ristaino revealed that the Gladiator Ghosts are indeed homosexual and in love with each other after "Morituri Te Salutamus" aired.
Kate Leth draws the Lady Lemongrabs as a couple. In the Fionna and Cake comic book, their relationship is only suggested through (admittedly obvious) subtext. Outside of the issue, though, Leth repeatedly draws the Lady Lemongrabs in obvious romantic scenarios.
Olivia Olson, the voice of Marceline, revealed that someone on the show's crew told her that PB and Marcy used to date, but that they can't outright say it on the show because of Moral Guardians and (most likely) the Russian government.
Word of God: Princess Bubblegum is actually made of bubblegum.
Princess Bubblegum's composition is actually a plot point in "Mortal Recoil".
BMO is "sexless", being a robot, and also genderless. S/He has been called masculine or feminine pronouns by different characters. For what it's worth, BMO is voiced by a woman, and the episode title "BMO Noire" uses a feminine spelling for the French adjective; however, that same episode has BMO imagine having a relationship with a female (chicken), while in another s/he pretends to be a "real boy."
Months after the airing of "The Red Throne", the crew confirmed at Comic Con that Flame Princess and Cinnamon Bun are not dating.
Adam Muto finally revealed what was Martin's cosmic crime at the finale's screening: turns out Martin went into space and kept conning people left and right until one of his cons caused some trouble with aliens, which resulted is his imprisonment at the Crystal Citadel.
Kent Osborne and Ghosthsrimp revealed at the Ghostshrimp and Friends Podcast that GOLB is absolutely powerful and the finale didn't show his full potential. They also revealed that Betty has total control of his mind after she fused with him.
Kent and Shrimp also revealed that Fern is still alive and inside the Finn Sword.
Working Title: Many of the episodes have had original titles that were changed. Some examples:
"The Royal Promise" → "Slumber Party Slaughter" → "Slumber Party Panic"
"Meet the Ice King" → "Prisoners of Love"
"Ice King and Son" → "What Is Life?"
"Return to Nightosphere" → "Marceline's Dad" → "Nightosphere" → "It Came from the Nightosphere"
Tree Trunks was based on as well as written expressly for Livingston, who is an old friend of Pendleton Ward's family.
Not so much a person, but a urinal where Penn works was the inspiration for the Cosmic Owl. The light reflects off the very shiny metal urinal and resembles the Cosmic Owl. This strange little tidbit of triva came from a interview with Nintendo Power.