"Book: Air" was a very common name for fan sequels, in keeping with the Theme Naming of the show's seasons, as it was the only main element remaining that did not have its own season. The first season of Korra is titled "Book One: Air".
When the series was initially announced as The Last Airbender: The Legend Of Korra, some fans rejected the Artifact Title and its association with the much-disliked film adaptation, instead referring to the series as The Legend Of Korra. Official sources soon followed suit.
Two of Aang and Katara's kids are named Kya and Bumi, after Katara's mother and Aang's oldest friend. Fanfiction writers named hypothetical daughters of Katara "Kya" years before The Legend of Korra was ever announced.
Fans have speculated that if airbenders weren't such adamant pacifists, they could be very effective at killing people by simply bending the air out of their lungs and making them suffocate. In "Long Live The Queen", Zaheer does just that.
Jinora Gran-Gran, I've been reading all about your old adventures; I've been dying to ask you; what happened to Zuko's mom? Katara: Well, Jinora, it's an incredible tale— Ikki:[interrupting] Gran Gran, you look old. How old are you? Why is it so cold in the South Pole? Can we sit around a fire and play games and tell scary stories and make snowmen? And then could you make the snowman move with waterbending and chase us? Wouldn't that be fuuuun? [Jinora hangs her head in disappointment]
Brolin for Bolin. Even more appropriate now that we know about his lady-killing ways.
Mama!Mako is becoming quite popular on account of Mako's doting and protective ways.
Sparkly Sparkly Bush Man for the park-dwelling vagabond Korra meets in the first episode (after Sokka's temporary name for Combustion Man of the original series). Secondary sources later revealed his real name as Gommu.
Korralition or Krew for the new iteration of Team Avatar, as their in-universe team name, the Fire Ferrets, wasn't known to the fandom until early March 2012.
Spider-Lin for Lin Beifong after her actions in Episode 6.
Many of the characters have earned themselves superhero themed nicknames. Lin has also been dubbed "Iron Lin" for the way she puts on her armor, and "Wonder Lin" both for being amazing and the fan theory that Toph created her via earthbending. General Iroh has earned the nickname "Iroh Man" after the finale, and Mako has been dubbed "Batmako" for his similarities to Batman in episode 3.
Big Daddies for the mecha tanks introduced in episode 7, especially due to the diving suit inspiration.
Korramobile for the Satomobile the Krew rides in when hunting Equalists in Episode 8 is somewhat popular given all the Batman undertones.
"Honora" for Zuko's daughter (the current firelord) who has yet to appear in the show.
Kai has already acquired the rather unfortunate nickname of "Shitstain", on account of him being an arrogant little twerp.
Before her name was revealed, a common nickname for Ming-Hua was "Lady Crazy-eyes".
Suyin's artistic son, Huan, has gained the moniker "Skrillex" from some fans, because they share some similiarities in appearance.
Before they were revealed as the Red Lotus, Zaheer, P'Li, Ming Hua and Ghazan were known - on this wiki - as the Irregular Benders. Other names could include the Exbendables or one could even call them the anti Team Avatar.
P'li in particular was called either the Combustion Woman or Sparky Sparky Boom Ma'am, as a reference to the man from the first series also capable of such a power.
Friday Night Death Slot: Book 2 aired Friday night instead of Saturday morning. By the numbers, it is down about 1-2 million viewers per episode than last season. And then they push it back another hour without warning, leading to another drop of a million viewers. Book 3 remained in the Friday night slot until it was taken off the air completely for an online-only release.
God Never Said That: Despite the quote from Andrea Romano being that the original cast might as well be dead, for all of the impact they'll have on the plot, numerous people still insist she declared the entire cast to be dead and gone, accusing her of being mistaken or lying when it was proved otherwise.
Genius Bonus: Astute viewers may recognize the Venom of the Red Lotus as mercury.
Episode 6: Lin was the third person in Tenzin and Pema's Love Triangle.
Episode 7: One of the Satos is working with the equalists. It's been a long time theory at least one of them is. Also, mechas. Super bonus points for those who saw the blue prints way back in episode 1. Also in-universe with Korra having eavesdropped.
Episode 9: Tarrlok is Yakone's son, and Amon has a means of protecting himself from bloodbending.
Thus far in the finale: Tarrlok is Amon's brother—his younger brother. Tumblr went on fire for that one.
And Amon is a bender—and a bloodbender.
Pretty much every major plot point was successfully predicted. It's only a matter of time before a waterbending Serial Killer named A. Firebender shows up.
Combined with Hilarious in Hindsight is that Avatar/Naruto crossover fics were common due do the fact that the designs weren't horribly dissimilar. Cue Studio Pierrot, Naruto's animation studio, animating for Book 2 of Korra.
"The Sting". Many people were not the least bit surprised that Varrick turned out to be a Corrupt Corporate Executive who staged the attacks on his own vessels so he could buy out Future Industries.
"Harmonic Convergence". Unalaq reveals his master plan, to become the Dark Avatar by merging with Vaatu like Wan did with Raava. Lots of people saw that coming a mile off, but most dismissed it because it was so ridiculous. Joke's on them, eh?
Book 3 - "In Harm's Way": When P'Li mentioned she had been locked up for thirteen years, some fans did the math and theorized that the Irregular Benders were imprisoned for attempting to attack/kidnap Korra when she had just been revealed as the Avatar. They were bang on the money.
"Long Live The Queen": Fans have long speculated on how utterly destructive airbending could be if its practitioners didn't use such a pacifistic style, with one of the most horrifying possibilities being sucking the air out of somebody's lungs. Come episode 10, Zaheer proved them right.
"Enter The Void": After a season of failing to metalbend, many fans began to speculate that Bolin would instead be revealed to be capable of lavabending. This got confirmed in this episode.
Name's the Same: There's a real person named Hiroshi Sato; a retired Japanese football player.
No Celebrities Were Harmed: While not closely visually related to their historical equivalents, some characters share features of famous people of the World War era.
Varrick's eccentric mannerisms, quick temper, and business layout are very similar to that of American media mogul William Randolph Hearst. In the episode "Peacemakers", he furthers the similarities by openly filming the civil war and splicing it with fake footage to make it propaganda, a practice Hearst used in the Mexican theatre of WWI.
The Earth Queen is a dead ringer for the Empress Dowager Cixi, known for her conservatism, autocratic rule, and - according to even the most charitable accounts - her immense wastefulness.
After getting his head shaved, Zaheer bears a striking resemblance to his voice actor Henry Rollins.
Playing Against Type: Steve Blum as Amon, Clancy Brown as Yakone, and Lance Henriksen as The Lieutenant are the only major exceptions so far. PJ Byrne starred in quite a few medical and/or legal dramas before being cast as Bolin. Mako's actor David Faustino was best known for his role on Married... with Children. Mindy Sterling (Lin Beifong) and Janet Varney (Korra) are best known for comedic roles. And while Dee Bradley Baker isn't new to voicing menacing villains such as Tarrlok, it's certainly not something he's necessarily well known for. There's also JK Simmons, best known for playing hilariously foul-mouthed, choleric Jerkasses, as Tenzin, the most calm and spiritual member of the cast (though he has his moments).
Bruce Davison, who specializes in sleazy or just plain weird characters, is the new Zuko.
Production Throwback: Naga the Polar Bear-Dog, Korra's animal guide and occasional transport for the new Team Avatar, was originally going to be Aang's waaaay back before the series was fully realized- sketches and concepts for this can be seen in the Avatar: The Last Airbender official art-of book.
Promoted Fangirl: Janet Varney was a big fan of the original series even before auditioning for the role of Korra, needless to say she was stoked to hear that she'd booked the part.
Reality Subtext: Probably not intentional, but it's been noted that the Book 3 premiere's title "A Breath of Fresh Air" is very apt, with many fans finding it a huge improvement after the Seasonal Rot of Book 2.
Screwed by the Network: Book 1 was aired on Saturdays with a great deal of promotion, and it got very high ratings. But for Book 2 the channel gave less promotion and moved it to the Friday Night Death Slot. The Book 2 premiere only had half the ratings of the Book 1 premiere. Then with little warning, the show was pushed back an hour and ratings fell in half again. See how bad the numbers got. Whether intentional or not, the network screwed this show hard.
When Bryan Konietzko announced the time change, he added that it may have been done to try and counter-act this. It kinda worked for episode 9.
Book 3 received shockingly little marketing for what's ostensibly the network's flagship show, with the return date only being announced a few weeks in advance. This may have been related to theShort Run In Peru leak of four Book 3 episodes. In any case, the ratings dropped even further. Then, after four weeks of new episodes, covering episodes 1 to 7, Nick pulled episode 9 from the schedule and moved the entire series to a weekly release on their website. Ironically, this was after a bizarre set of ads that asserted the season could only be seen on television.
Short Run In Peru: Kinda. Several episodes of the Spanish dub of Book 3 were leaked onto the internet before Book 3 aired anywhere. This may have caused Book 3 to air prematurely with little marketing.
Throw It In: A scene in "The Spirit of Competition" where Mako is angrily walking through a door and completely ignores a fan trying to say hi ("Hey Makooooo-oh") originated when someone drew a random extra standing next to Mako in the animatic and the episodes director thought he looked disappointed.
There was an In-Universe case in a mover where Bolin kisses an actress in a scene where he wasn't supposed to and the director decided to keep the kiss.
Jinora: I've been dying to ask you: what happened to Zuko's mom?
Katara: [epic theme music begins to swell] Well, Jinora, it's an incredible tale—
Ikki: [theme cuts off] Gran-Gran, you look old! How old are you?
There's also something pretty suspect about releasing a trailer that features Korra and Mako kissing the day before April Fool's, even if it actually did happen.
It feels like the episode "The Spirit of Competition" was trolling all the shippers at once.
The reveal that Toph's daughters have different fathers feels like this. Ever since Lin's introduction much speculation has gone into who her father is, but the fact that neither her nor her sister knows who their respective fathers are has opened the door for a whole slew of speculation, no doubt sparking shipping wars by the mere implication that the popular Tokka ship is in some way or form canon. And if one didn't care about that, there's the fact that the creators can potentially give viewers a Mamma Mia!: show potential candidates and imply heavily who's father is whom, but then leave it open to interpretation at the end. Also recall that Toph is revealed to be potentially alive, but the future is dark and Mike and Bryan has the entirety of Book 4 to toy with fan expectation.
Korra Nation. The point was to get people to inform their friends of the show by having automatic posts show up on you Facebook/Twitter profile for people to click. The person sending the posts earned points for every link clicked and every person who signed up using their personal link, with the points going towards prizes including a drawing for a trip to this summer's SDCC and exclusive MP3 releases of music from the show.
Another branch of Korra Nation dealt with gaining likes, shares, and tweets of the Korra Nation website; on which fans could discover hidden content such as production sketches and background art. Sharing the site 100,00 times would allow fans to see the premiere a week early. It earned 100,000 points within the first week of its announcement, and as promised the first two episodes were available online on March 24th.
The Korra Nation website no longer exists, but the viral marketing continues with the Korra Nation tumblr and facebook pages. Art, production information, and clips of the upcoming episodes are posted to these pages once or twice a week.
Asami Sato was originally intended to be a villain, but during the first season's scripting process Mike and Bryan decided that 1) she wouldn't have much use in the story after her intended mid-season villainous reveal, and 2) was too cool a character to waste that way.
There were plans to revisit the "foamy mouth guy" gag from the previous series, with the twist that the crazy fan was rooting for Amon instead of the heroes. It got dropped because they felt that the joke clashed too much with Amon's general creepiness.
Word of God: Mike and Bryan clarified a number of details concerning events that bridge the two series, such as who's ruling the Fire Nation in Zuko's stead and why Aang was only in his 60s when he died.
It was later clarified due to potential ambiguity that Ghazan and Ming-Hua were both killed.
Working Title: First Avatar: Legend of Korra, then The Last Airbender: Legend of Korra. The "The Last Airbender" Artifact Title was ultimately dropped, while the "Avatar" supertitle was retained for overseas markets.