Book of Elements

The Book of Elements arc is the fourth arc in the LEGO Ninjago series. Every installment is an Elemental titled "chapter" that focuses on one or multiple Ninja. Each season builds the plot up to the final confrontation with the Crystal King.

After facing the greatest evil the world will ever see, the Ninja have some down time. Each season in this phase "retells" the original seasons of the past through the enemy variety, almost in the right order. This phase is often referred to the soft reboot era of Ninjago, with a new set of writers, changing animation studios, shortening episodes to 11 minutes, and dropping the "Masters of Spinjitzu" subtitle. Additionally, each season incorporates a certain Elemental theme dubbed "chapters." The Book of Elements refers to how each section dedicated to one Ninja's Elemental Power is referred to as a chapter.

The Elemental chapters, in order, are Fire, Ice, Lightning, Earth, Energy, Water, Creation, and Destruction.

The seasons the arc is made up of are the Secrets of the Forbidden Spinjitzu, Prime Empire, Master of the Mountain, The Island, Seabound, Virtues of Spinjitzu, and Crystalized. It is tied with the Master Trials arc as the longest arc by installment count, with a total of seven.

It is preceded by the Oni Trilogy and succeeded by Ninjago: United.

Fire Chapter - Secrets of the Forbidden Spinjitzu (2019)
The Scrolls of Forbidden Spinjitzu have been kept a secret for a thousand years. With good reason. The evil Serpentine sorceress, Aspheera, was banished along with the Scrolls – but now she is back, hungry for revenge, and ready to get her fangs on the Scrolls once more and reclaim her powers. The ninja’s powers, friendships, beliefs and loyalties will be put to the test like never before.

Ice Chapter - Secrets of the Forbidden Spinjitzu (2019)
Zane’s been captured by the evil Ice Emperor. The Ninja have mounted a desperate rescue mission – but if they want to see their friend again, they’ll have to battle hordes of Blizzard Samurai as they make their way through the Never-Realm, from where no Ninja has ever returned.

Kai is the focus character of this season, and Aspheera and the Ice Emperor are the main antagonists. The Pyro Vipers and Blizzard Samurai serve as the villainous factions. Zane and Kai get center focuses, and its villainous factions are retellings of the Serpentine and Stone Samurai Warriors from Seasons 1 and 2. The collectible item for this season are the Scrolls of Forbidden Spinjitzu.

Lightning Chapter - Prime Empire (2020)
In the hyped video game, Prime Empire, you can be whoever you want to be. Jay, ever the avid gamer, can’t wait to start playing. But when hundreds of players, and Jay, suddenly start vanishing without a trace, the ninja need to get inside the game and find out who is playing Unagami. Now they must compete in adventures and difficult game worlds, win all three Key-tanas– and only then can they face the evil Unagami. Can they reach the final level and beat the game?

Jay is the focus character of this season, and Unagami is the main antagonist. The Red Visors serve as the villainous faction. The villainous faction retellings are the Nindroids in the Red Visors. Jay is the focus character, as this season delves into his obsession with video games, and how he makes his way through the digital world of Prime Empire to save his friends. The collectible weapon for this season are the Key-Tanas.

Earth Chapter - Master of the Mountain (2020)
The Ninja are invited to the beautiful Shintaro Kingdom to celebrate the young Princess Vania’s birthday. At first glance, the Ivory City looks like a pristine place, but the Ninja soon uncover a dark, obscure, long-forgotten underworld: The Dungeons of Shintaro. Once inside, they must fight their way to freedom through a maze of tunnels paved with dangers and strange creatures ruled by the merciless Skull Sorcerer. The Ninja must choose their path wisely…

Cole is the focus character of this season, and the Skull Sorcerer is the main antagonist. The Awakened Warriors serve as the villainous faction. The villainous faction retellings are the Ghosts in the Awakened Warriors. Cole is the focus character, as this season delves into the past of his mother and her relationship with Shintaro Mountain and her Elemental Power. The collectible weapon for this season are the Blades of Deliverance.

Energy Chapter - The Island (2021)
An expedition led by Lloyd's mother has gone missing on a remote island off the coast of Ninjago. The Ninja go on a rescue mission, and they recruit Twitchy Tim, the only person who has returned alive from this mysterious island. They track down the expedition but at the same time discover an ancient tribe of native islanders with a strange lightning-based technology. This tribe fears and worships a terrible sea creature. They manage to keep her submissive through frequent and precious sacrifices, but her anger arouses, and she demands more.

Lloyd is the focus character of this season, and Chief Mammatus is the main antagonist. The Keepers of the Amulet serve as the villainous faction. The villainous faction retellings are the Anacondrai Cultists in the Keepers of the Amulet. Lloyd is the focus character, as this season keeps track of his journey to rescue his mother from the Island of the Keepers. The collectible item for this season is the Storm Amulet.

Water Chapter - Seabound (2021)
If you’re ready for the challenge, just hop on board their newly designed underwater ship, the Hydro-Bounty and let’s get this mission started! Along with Nya’s mom, Maya, P.I.X.A.L., and her fellow ninja, Jay, Zane and Lloyd, you’ll join Nya in a battle against the elements and the evil Prince Kalmaar, the Prince of Merlopia. That’s when things really get tricky. He has an evil plan to awaken an ancient sea-serpent, Wojira.

Nya is the focus character of this season, and King Kalmaar is the main antagonist. The Maaray Guards serve as the villainous faction. The villainous faction retellings are the Sky Pirates in the Maaray Guards. Nya is the focus character, as this season goes into detail with her relationship with her mother and the history of the Elemental Power of Water. The collectible item for this season is the Wave Amulet.

Destruction Chapter - Crystalized (2022)
The Ninja are back for another season with brand new adventures in NINJAGO®: Crystalized! This time they have been locked up in Kryptarium Prison where they are surrounded by some of their old enemies. Here they learn a mysterious Crystal King is recruiting a council of evil enemies. To find out the identity of this new enemy, they escape from prison and become fugitives. Who is the Crystal King? Why is he gathering a powerful counsel? Get ready for another action-packed mission with the ninja!

Lloyd appears as the mascot Ninja, and the Crystal King is the main antagonist. The Vengestone Army serve as the villainous faction. The villainous faction retelling is the past villain's ghosts in the Council of the Crystal King. The collectible items in this season are the Weapons of Destruction.

Series Impact

 * This season takes place months after the end of March of the Oni.
 * Zane's visions of the Green Ninja and the Titanium Dragon are mentioned by Jay in the first episode.
 * The Ninja play the video game Lava Zombies throughout the season, and mention the name of its creator, Milton Dyer. He would become more important in the next season.
 * The Pyro Vipers are revealed to be an ancient tribe of Hypnobrai that lived in the Serpentine Highlands when Garmadon and Wu were young. It is unknown how they received the ability to absorb Elemental Power, but it is possible that it was done with Aspheera's sorcery skills.
 * Forbidden Spinjitzu is a concept revealed in this season. It is an ancient martial art that the First Spinjitzu Master created in order to reach ones True Potential in an instant. It is a dark power that is able to corrupt those that use it.
 * Clutch Powers makes his first official appearance as a character in this season after having been alluded to in Season 1. It was first said that he discovered the Silver Fangblade that got turned into the Blade Cup, but since then he has lost his mojo for exploring and has been burnt out.
 * Funnily enough, in the episode that Clutch is first mentioned, Lloyd explores an ancient Serpentine Pyramid. In the first episode he is formally introduced, the Ninja explore an ancient Serpentine Pyramid.
 * These pyramids are not the same, however, as one is in the Sea of Sand and the other is in the Desert of Doom.
 * While the Ninja are in the Desert of Doom, Zane discovers the Teapot of Tyrahn in the belly of Beohernie. It is unknown how it got there, but it presumably went from the scrapyard from Season 6 to some dump where it might have been consumed by the giant beetle. When Zane is spit out of the beast, so too is the teapot.
 * The Ninja visit Acidicus and Skales in the sewers after not seeing them since The Hands of Time. This continues the idea that Acidicus loves history, as he was the one to share the legend of the Golden Master, and now the story of Aspheera and the Treacherous Deceiver.
 * When trying to figure out a quest to go on, the Ninja decide between which old villains that are still around to go after. They mention Garmadon, who disappeared at the end of the previous season, the Sons of Garmadon, who are incarcerated in Kryptarium Prison, Chen, who's soul was returned to the Departed Realm during Day of the Departed, and Pythor, who's current whereabouts are unknown.
 * In the episode Questing for Quests, the Commissioner is pointed out for always working on that model ship, and never making any progress. This may be a reference to the "floating timeline" nature of the show and many other animated series.
 * The Preeminent is brought back from the Departed Realm in the episode The Kaiju Protocol. This confirms that when the Cursed Realm was destroyed, all of the ghosts inside it, including the Preeminent herself, entered the Departed Realm. She is brought back, briefly, and defeated by P.I.X.A.L., then returned to the Departed Realm.
 * The Never-Realm is introduced this season. Supposedly the furthest realm away from Ninjago, and the hardest to get to. Zane is marooned in this realm by Aspheera's powers, and is found by Vex, who coerces him into becoming the Ice Emperor. There are a few discrepancies in the story presented. Canonically, Zane was blasted 60 years into the past when he arrived in the Never-Realm, which means he reigned as the Ice Emperor for that long, canonically, since before the beginning of the series. However, it is presented in the story as though time goes by much faster in the Never-Realm than it does in Ninjago. This would explain why when the Ninja arrive only a day or so later, 60 years has passed since Zane's arrival.
 * Desipite having his memory totally erased, Zane regains all of his memories and returns to perfect working order just after hearing the words "protect"...
 * At the end of the Fire Chapter Aspheera is placed in the same jail cell as Garmadon in the episode The Darkness Comes.
 * This season mentions a location in the Never-Realm called Mala-Wojira, said to be cursed by a storm spirit known as Wojira's Wrath. This is the second season to name the storm spirit Wojira (the first being Sons of Garmadon, where she is referred to as "Wohira.")
 * Because of the connection between this creature and the realms, it's possible that Wojira either originates from the Never-Realm or word of her destructiveness has reached other realms.
 * The Mechanic, one of Ninjago's villains, is seen locked up in Kryptarium Prison in this season, presumably put there after his battle with Kai & Zane in Season 8.
 * Sons of Garmadon members Killow and Ultra Violet are seen locked up in Kryptarium in this season, having been locked up here since the events of Season 9.


 * This is the first season to feature Airjitzu since Season 7, although this season's Airjitzu is not real or physical, but rather a power-up in the game. This explains why it's able to be used now, when it is seemingly forgotten otherwise, because it is digital it does not rely on Edo magic.
 * Cole uses the dance move Triple Tiger Sashay in this season during a dance off. He was taught this move by his father when he was growing up and performed it during the talent show in The Royal Blacksmiths.
 * The password to enter Superstar Rockin' Jay's hideout is "Mr. Cuddlywump," which is the name of Jay's stuffed teddy bear, that is first mentioned in The Hands of Time.
 * Certain Wack Rats have the Sons of Garmadon insignia crossed out on their back. This likely doesn't mean much, just to show that they are wearing their old outfits.
 * The Teapot of Tyrahn makes its reappearance in this season, after having been coughed up by Beohernie Clutch Powers is seen holding it in the intro to the first episode and disappearing in a puff of orange smoke afterward.
 * The location Buddy's Pizza in Ninjago City makes a return for the first time since the Season 2 episode, "Child's Play."
 * Kai's Avatar design is reminiscent of his Red Shogun outfit from the first episode of Season 4.
 * Similarly, Superstar Rockin' Jay's design seems to be inspired by the flashy outfit that Jay wears as a TV show host in that same episode.
 * Zane's Avatar outfit, while it doesn't appear in the show, is a reference to his pink ninja gi that is seen in the Season 1 episode, "Can of Worms."
 * Similarly, Cole's avatar outfit also doesn't appear in the show, but it is a reference to Rocky Dangerbuff's design from Season 8.
 * At the end of the season, Unagami in child form, Okino, and Racer Seven all enter Ninjago and begin to live there.
 * When Cole begins to fall down the Cliffs of Hysteria he says, "Oh no not again!" this is a reference to "The Fall," when he literally fell down and was presumed dead. This becomes a recurring joke in the series where Cole falls at some point.
 * The Mechanic returns in this season, after somehow breaking out of Kryptarium Prison between seasons.
 * He drives a Mr. Chen Noodles truck as a getaway car.
 * It is revealed that Milton Dyer was developing several sequels to some video games that have been mentioned in the series before like Fist to Face 4 and Ukelele Legend.
 * Lloyd faces off against a digitally recreated memory of Harumi in Stop, Drop and Side Scroll. He reminisces on their time together and thinks she can be trusted but is ultimately defeated by her. This shows that he still has feelings for her and is traumatized by what she put him through.
 * In The Prodigal Father, Zane is referred to by the Mechanic as "the Titanium Ninja," a term he has not been referred to very many times since Possession.
 * In the final battle with the Empire Dragon, Jay connects with Unagami by telling him that he too was abandoned by his parents, referring to how his father Cliff Gordon left him at Ed & Edna's doorstep, and how his mother mysteriously vanished.
 * Several Kryptarium inmates are broken out of jail this season, including the likes of Captain Soto and Ultra Violet. As of now, Soto's fate remains unknown, and it is revealed in the Garmadon comic series that Ultra Violet works under a new master.


 * Lloyd mentions the Teapot of Tyrahn in the season premiere, asking if it has been found.
 * This marks the third time that the Teapot is mentioned in a row.
 * Curiously, Lloyd does not remember the events of Skybound, so it's possible he knows what it is because Jay or Nya told him.
 * Lloyd also wonders if someone has found either Pythor or his father, confirming that they have been missing since Day of the Departed and Endings respectively.
 * Cole is playing an updated version of the video game "Prime Empire" in the first episode, saying that Unagami and Milton Dyer fixed it so it can be playable without getting trapped inside.
 * This season takes place over less than a month, seeing as in The Island, only one month had passed between Season 12 and "Uncharted."
 * Cole's mother, Lilly, is finally named. It is revealed that she was the previous Master of Earth and that her father (Cole's grandfather) fought in the Serpentine War.
 * It is also revealed that she died of an illness when Cole was younger. It was implied in Season 8 that she had passed away prematurely, which led to Cole becoming distant from his father.
 * "Spinjitzu Burst," the fourth alternate martial art to Spinjitzu, is revealed in this season. It is described as immense power that makes your Elemental Power grow when you are surrounded by your element (in this case, it was under a mountain, surrounded by Earth.)
 * It is also revealed that Cole's mother attempted to harness this power by visiting the Heart of the Mountain, a temple built for Earth Elemental Masters to grow their power. She died before she could do this.
 * Cole's falls in The Fall and The Cliffs of Hysteria are referenced in the episode "The Real Fall," which is meant to be a gag on the fact that Cole is always falling.
 * Metalonia, the homeland of the Master of Metal Karloff, is mentioned for the first time since Season 9. It is also shown off for the first time.
 * When Kai mentions the time Zane impersonated Clutch Powers to get into the Explorer's Club, he is referring to the events of "The Explorers Club."
 * At the beginning of this season Master Wu is depressed that he is too old and can't do much. This prompts the Ninja to invite him on their journey to Shintaro, which he obliges. In the season finale Wu says that he is ready to go on another adventure, not wanting to slow down. This is foreshadowing him journeying to the Island of the Keepers with Misako and Clutch Powers in the next installment.
 * It is revealed that the Skull Sorcerer was enslaving the Geckles and Munce to mine copious amounts of Vengestone, which are to be sold to some mysterious "buyer." His plans are foiled, and the buyer's identity is never revealed in this season.
 * It is revealed in Crystalized that the Vengestone buyer is actually the Crystal King.
 * When the Ninja first meet Princess Vania she mentions several events from the past seasons.
 * She asks them if it is true that they have been to Hiroshi's Labyrinth, but the only Ninja who actually went there was Lloyd in Season 3.
 * She also asks if they've competed in the Tournament of Elements.
 * Lloyd is suspicious of Vania when they first meet, still being traumatized by Harumi's deceit in Season 8.
 * Jay & Nya's Yin-Yang Court is mentioned for the first time since March of the Oni.


 * Ronin makes his reappearance this season after being absent since Season 9. As per usual he's up to his old business.
 * Wu being with Misako and Clutch in the premiere episode was foreshadowed in the previous season when Wu declared that he wanted to go on another adventure (after the one he had in Shintaro.)
 * Fugi-Dove is confirmed to have been captured by Ronin in the first episode after having broken out of jail in the episode Level Thirteen.
 * Curiously, he is not seen in the finale with the other inmates.
 * The storm spirit Wojira is officially revealed as a real creature that exists, after having been foreshadowed in Season 8 and Season 11.
 * It is revealed that the Keepers who inhabit the titular island were guardians of a sacred Storm Amulet. They were placed there by the First Spinjitzu Master to keep the amulet away from Wojira, who is said to have existed "long before Time had a name," (a reference to the iconic beginning prologue speech from Wu in Season 1.)
 * This is the first introduction to the Amulets of Wojira, with the Storm Amulet taking center focus in this season.
 * The Wave Amulet also appears on her head when Wojira is shown at the bottom of the sea in the finale episode.
 * This also sets up the next season, as it is revealed that it was placed there by Prince Kalmaar in an attempt to awaken it.
 * Jay remarks that his parents used to call him "their little gift," referencing the fact that he was literally dropped on their doorstep when he was a baby.
 * At the end of the installment Clutch Powers attempts to steal the Storm Amulet but is caught, and the amulet is returned to its shrine. It's revealed in the next season that this amulet is a fake, and he swapped it out for the real one before he was caught.


 * Unagami and Okino from Season 12 make their reappearance in this season.
 * The Teapot of Tyrahn returns in this season after being absent in The Island. This continues the trend of the teapot appearing in almost every installment since Season 11.
 * The teapot is seen on display at the Explorer's Club headquarters, implying that after Clutch Powers found it in the Desert of Doom, and the Ninja realized it was missing, he put it on display. At the end of the episode that it appears in, it is flung out of the building when Wojira crashes into it.
 * Kai & Nya's parents, Ray & Maya, appear in this season for the first time since their introduction in The Hands of Time. It is implied through words of the writers off-screen that the married couple went on a well-deserved vacation after being freed from the clutches of Krux. Krux himself is also mentioned for the first time in the first episode after being mentioned previously in Season 8.
 * This season reveals massive amounts of lore that dates back to before the beginnings of Ninjago, which had never been previously explored.
 * Previously, it was known that the Golden Peaks existed before "Ninjago," as it is traditionally known, and the First Spinjitzu Master used the molten gold in the mountain to form the Golden Weapons of Spinjitzu to create the landmass that would become Ninjago and the Dark Island.
 * It is revealed in this season that the realm that Ninjago is in existed long before the First Spinjitzu Master's arrival and was a planet of mostly ocean and storms ruled by Wojira. The Merlopians were the primary sentient life forms on the planet.
 * The First Spinijtzu Master commanded all of the Elemental Powers except for Water and Wind, which belonged to Wojira. In order to create a peaceful world, the First Spinjitzu Master created the Keepers and enlisted the help of the Merlopians to defeat Wojira and calm the seas. With their help, he pries the Storm and Wave Amulets off of Wojira which plunges her into a deep sleep. He gives the Storm Amulet to the Keepers to protect, and the Wave Amulet to the Merlopians.
 * This means that Wojira and the Merlopians predate the existence of "Ninjago" itself. The creation of Ninjago was originally the beginning of the timeline.
 * Because the First Spinjitzu Master commanded all the Elements except for Water and Wind, it is possible that this is why those two Elements were left out of Clouse's spell to turn everyone into an Anacondrai.
 * The First Master of Water is revealed to be a Merlopian named Nyad. This makes Maya, Kai, & Nya descendants of Merlopians.
 * If Maya knew about her Merlopian ancestry, it's possible she named Nya after Nyad.
 * In the pilot episode, the villain Miss Demeanor is seen attempting to steal mass amounts of Vengestone for some unknown reason. This is the second instance of mass amounts of Vengestone being exported to some mysterious place, after the Skull Sorcerer reveals that he has been getting paid by a "buyer" to mine the Vengestone in the dungeons of Shintaro.
 * In Crystalized it is revealed that the Vengestone buyer is the Crystal King.
 * At the end of the season, Nya becomes one with the Endless Sea, literally becoming Water. She leaves the Ninja team as she is called to the sea.
 * The Ninja all say their goodbyes, and several previous characters in the series pay their respects to her, making it out like she was killed.
 * It may be implied that she could somehow come back, as it is said that the First Master of Water, Nyad, also became one with the sea, but since Nya is her descendant, she had to come back somehow to have children. This is pure speculation.
 * This new form that Nya takes is referred to as "NRG Nya" in the sets. This adds to the collection of NRG Ninja (or True Potential Ninja) that was originally started in Season 1, when each Ninja became one with their Elemental Power.
 * Kai neglects to join Nya, Lloyd, Jay, & Zane on their mission underwater. The reasons given are that Wu needed to study the current and previous Masters of Fire, but it could also be a nod to the fact that Kai is afraid of water, as revealed in Possession.
 * One of the ice-cream flavors that the Dairy Dragon apparently sells is called "Bananakhan," named after Nadakhan the Djinn.
 * Since the events of Skybound were erased from the timeline, those events must have become public knowledge due to Jay and Nya telling everyone.
 * Kalmaar references the Oni, revealing the fact that the initial Oni invasion on Ninjago is common knowledge in Merlopian history.
 * This also marks the first time the Oni are mentioned since their debut.
 * He also mentions the Vermillion, but it is unknown how he knew about that species of Serpentine.
 * A Ninjago City tour bus points out Borg Tower to tourists, telling them it was the site of many battles including one with Garmadon (referencing the events of Hunted,) and with Unagami (referencing the events of Prime Empire.)
 * Battles they failed to mention include the two with the Overlord, which took place in that same spot.
 * Patty Keys returns for the first time since Season 2.


 * It has been one year since Nya's disappearance, and all the Ninja are taking it a different way. Zane and Cole remain at the Monastery, but Zane has turned off his emotion switch to increase productivity.
 * Kai has become a teacher at his own school, teaching kids to run into battle and destroy the enemy without thinking.
 * Lloyd has resulted in cleaning windows in Ninjago City.
 * Lloyd cleaning windows was foreshadowed in a chapter of The Splinter in the Blind Man's Eye when he tells Clancee, "I am not going to be cleaning any windows or anything else. My priorities are greater than that."
 * Jay has become a recluse and started living in Dr. Julien's lighthouse.
 * This mimics the beginning of Season 4 when the Ninja split up after the loss of Zane.
 * This marks the first appearance of the lighthouse since Season 6.
 * Even after one year, the Vengestone smuggling continues.
 * The mayor has hired a new group of Ninja to handle the threat, known as the Neon Ninja, to combat this.
 * It is also mentioned that since Seabound, Benthomaar has succeeded his father as the King of Merlopia.
 * Nyad's physical form is shown off for the first time. She helps Nya regain her memories, and in a flashback, her death in the undone Skybound timeline is shown.
 * Since the First Master of Amber's appearance in Amber Spiral, this marks two of the first Elemental Masters being shown.
 * The Ninja use Aspheera's staff to turn Nya human. They were reminded to do this after Kai got his powers taken from the same staff.
 * After her powers are taken, she returns to normal, and she feels powerless to help the Ninja out of prison. Wu reminds Skylor that no one can ever be powerless. This is a reminder that even after Kai's powers were drained in the same way, they were able to return sometime later.
 * Aspheera returns this season after being arrested in Secrets of the Forbidden Spinjitzu. After she helps save Nya and escapes, she is recruited to join the council of the Crystal King by Harumi.
 * The mayor makes reference to several times the Ninja have indirectly caused danger to the city, namely the Oni Invasion, Aspheera's attack, Prime Empire's invasion, and Kalmaar's invasion.
 * In Dareth's defense against the Ninja, he recalls the times the Ninja saved the city from Garmadon, Unagami, and The Quiet One.
 * In the case of Harumi, she didn't actually take over the city, but she had a hand in it
 * Skylor returns in this season, after having last appeared at the end of Seabound to mourn Nya, and after her last speaking role in Hunted.
 * It is revealed that her power of stealing powers fades after some time.
 * Dwane, who was originally a junior member of the Explorer's Club, now works for the mayor.
 * After regaining her memories and losing her powers, Nya remembers her greatest fear of being normal from looking at the Mirror of Fears in "The Explorers Club."
 * In the vaults below Borg Tower, Cole and Jay go to steal Aspheera's Staff. There, Cole reminds Jay that in these vaults are the Sword of Sanctuary (last seen in March of the Oni,) and the Oni Mask of Vengeance (last seen in Hunted.)
 * It is revealed that since their powers dampened at the end of March of the Oni, the Golden Weapons of Spinjitzu have been kept in the Samurai X Cave at the Monastery. However, as it is reminded throughout the past few seasons, it's impossible to truly lose all power. (Such is the case with Kai in SotFS, Nya currently, and Skylor.)
 * After their power is returned to them and they come together, the weapons are destroyed and the powers within them are released. They take form into the Golden Utra Dragon.
 * Wu's age is made direct mentioned by him, as he tells Aspheera that he is "thousands of years old."
 * Ultra Violet, Ronin, and Captain Soto are shown to be imprisoned in Kryptarium again. Soto and Ultra Violet haven't been seen in the show since Prime Empire, meaning both of them have been arrested since then, and Ronin remains there after being arrested in The Island.
 * Ultra Violet being in prison means that she was either put there some time after the events of Garmadon, or that this season takes place before it. Later events seem to decanonize the events of Garmadon, so Violet being in prison makes no difference.
 * King Vangelis returns this season after having been imprisoned in Master of the Mountain. He is recruited into the Council of the Crystal King by Harumi.
 * Pythor returns this season after last being seen in Day of the Departed and Pythor's Revenge. He was last mentioned in Master of the Mountain as having been on the run, but it is revealed that he was defeated and captured by the New Ninja. He is later broken out of prison and recruited to join the Council of the Crystal King by Harumi.
 * Zane uses his human cloak for the first time in this season since March of the Oni, making it the first time he has used it in the Book of Elements Arc.
 * Twitchy Tim and his gas station return in this season after last appearing in The Island.
 * Krux, Acronix, and Garmadon are mentioned in this season when the Ninja speculate as to who will be joining the Council of the Crystal King, but Lloyd recalls that the three of their whereabouts are unknown.
 * This confirms what we've known about the Time Twins for some time, that their disappearances at the end of Golden Hour are ambiguous.
 * It also likely means that the events of Garmadon take place before this season, as the Ninja still don't know his whereabouts either.
 * Kabuki Mask, the masked person who recruited Vangelis, Pythor, Aspheera, and the Mechanic to join the Council of the Crystal King, is revealed to be Harumi.
 * This marks her first physical appearance since Saving Faith in Season 9, not counting Avatar Harumi's appearance in Prime Empire.
 * It is shown in Episode 13 that she died in the fall, but in another realm met with the Overlord, who gave her new life and new purpose. It is shown that following her revival, she returned to the Oni Temple and placed a crystal in the pedestal of the Mask of Hatred, which erected many other crystals in the temple. One of them showed the image of the Crystal King, who is revealed to be the Overlord.
 * In this flashback it is also revealed that the Crystal King sent Harumi to make him an army out of the enemy's weakness, (Vengestone.) It is shown that Harumi had been giving money to King Vangelis in Shintaro in exchange for large amounts of Vengestone, revealing that their operation with the Crystal King has been going on for at least a year or two. Additionally, Harumi was meeting with Vangelis in the moments before the Ninja's arrival in Shintaro and happened to be there while they spoke to the King.
 * The Ninja faulted her plans for now, but later picked the operation back up while enlisting the help of Miss Demeanor. The shipment that they delayed at the beginning of Seabound happened to be one of the last ones.
 * It is also revealed that Lloyd actually attempted to save Harumi after the building fell on her, but she was no longer under the rubble.
 * Harumi tells Lloyd that the Crystal King's ultimate plan is to steal the Golden Weapons of Spinjitzu, which have been under the Monastery since the end of March of the Oni.
 * In the Council of the Crystal King, an updated model of Mr. E is seen, who is referred to as Mister F.
 * In the episode The Council of the Crystal King, Clutch Powers can be seen holding onto the Teapot of Tyrahn. This marks the fifth appearance of the teapot in the Book of Elements Arc, having first appeared in the belly of Beohernie in Secrets of the Forbidden Spinjitzu, then later held by Clutch in Prime Empire, wondered about its whereabouts by Lloyd in Master of the Mountain, and then being seen at the Explorer's Club in Seabound.
 * The only installment in the Book of Elements Arc it has not appeared in at all is The Island.
 * The character Sally that appears in The Benefit of Grief is reminiscent of another character named Sally who was originally featured in Season 3. Both of them wear similar glasses and share a name, so it's not implausible that the girl in Master Wu's class from Rebooted grew up wanting to be a singer and dyed her hair pink.
 * Lloyd uses his Oni powers for the first time in Episode 14, revealing that like his father, his Oni power is fueled by anger. This marks the first time Lloyd uses the Element of Destruction.
 * The Samurai X Cave appears for the first time in this season, the first time in the WildBrain seasons, and the first since Secrets Discovered in Season 7.
 * When Lloyd meets the Overlord for the first time again, he calls back to Lloyd saying, "It ends now," in "Rise of the Spinjitzu Master." from Season 2.
 * The Overlord reveals that his new plan must be to "crystalize" the Ninja in order to stop them fully, because if he was to destroy them, their powers would take on new hosts. This fully confirms the concept that Elemental Powers may "find" new hosts when they lack one. It was originally merely hinted that was the case by creators in regard to Morro's power of Wind, but this confirms it outright.
 * It's revealed that since March of the Oni and Garmadon, Garmadon has been living in an apartment with NGTV's Vinny and has been sending Wu newspaper clippings forewarning him of the Overlord's immanent return.
 * The episode Christofern actually decanonizes the events of the Garmadon comic. It's revealed that instead of encountering Lord Mogra and the Red Crows to find himself and learn empathy, Garmadon instead began living with Vinny right after the events of Season 10 and learned empathy by taking care of a potted plant he named "Christofern."
 * The Crystal Army's weakness is revealed to be pure Dragon or Oni power, demonstrated by Garmadon who harnesses this. Lloyd being part Oni makes him also able to achieve this feat.
 * Quanish the Elder, Fenwick's brother, is said to have created a prophecy about achieving the Dragon forms, the opposite of an Oni form. This is a reference to The Splinter in the Blind Man's Eye Chapter 11, which dictates the point where Quanish wrote this scroll.
 * In Compatible, Kai flirts with Skylor using the same technique he taught Jay during Episode 1 of March of the Oni.
 * Following Season 12, Racer Seven has renamed herself Blazy H. Speed.
 * It is stated by the Overlord, which was already hinted at since Season 2, that the Great Devourer was corrupted by himself, which was part of his design to corrupt Garmadon to become his vessel. While it was known that destiny would lead Garmadon and the Overlord together all that time ago, it was never specifically stated until now that the Overlord himself created the Great Devourer.
 * At the end, the Overlord is defeated for good, and the original four Ninja's powers leave them to go back to where they came from. It is hinted that they may return some day.
 * The Virtues of Spinjitzu episodes show Wu using his Creation powers to the fullest extent we've ever seen it, being able to manifest entire locations and beings and impress them on the Ninja.
 * The flashback in which Lilly dances with Lou in The Virtues of Spinjitzu may be inspired by Way of the Departed, where it is mentioned in Chapter 3 that Lilly and Lou often danced outside on the terrace of their house, and Cole secretly watched.

Trivia

 * Every main antagonist in each chapter has been royalty of some kind.
 * Aspheera, the Queen of the Pyro Snakes
 * the Ice Emperor
 * Unagami, Emperor of Prime Empire
 * The Skull Sorcerer, King of Shintaro
 * Chief Mammatus
 * King Kalmaar
 * The Crystal King