Departed Realm

The Departed Realm is one of the Sixteen Realms. The dimension is where the souls of beings from all known realms, including the Cursed Realm, Ninjago, and the Underworld, go to after they die. It is the one realm that is impossible to access through any normal means, including the Realm Crystal.

History
At some point in time, the Departed Realm came into existence as one of many realms parallel to Ninjago. All of its deceased—save for the wicked and cursed, and disgraced warriors unable to come to terms with their death—would have their souls sent to the realm upon death, where they would rest in eternal peace unless disturbed.

Later, when the First Spinjitzu Master created the Realm Crystal, he was unable to connect its powers to the Departed Realm, with the artifact lacking the sheer power to do so.

The Last Voyage (Flashback)
Samukai, desiring an inventor to manufacture weapons of war for the Skulkin army, used Resurrectea to revive Dr. Julien, bringing his soul from the Departed Realm and returning it back to his body in Ninjago.

Weapons of Destiny
Attempting to wield all four Golden Weapons at once, Samukai was quickly overwhelmed by the power and disintegrated in the attempt. With his form in the Underworld destroyed, Samukai's lost soul was left to drift to the Departed Realm instead.

Pirates Vs. Ninja
Having recently created the Mega Weapon, Garmadon attempted to figure out its abilities and in the process accidentally wished for Captain Soto and his crew of Pirates to come back to life. Drawing upon Garmadon's power and energy, the Mega Weapon brought back the souls of Captain Soto, No-Eyed Pete, the First Mate, and the rest of the crew from the Departed Realm. However, one of the resurrected souls, attempting to wrest the Mega Weapon from Garmadon's hands, would be destroyed by the overwhelming power and sent back to the Departed Realm once again.

Rise of the Spinjitzu Master
After Lloyd defeated the Overlord with his Golden Power and purified all of Ninjago, Kozu and the entire Stone Army were all destroyed and sent to the Departed Realm.

Sometime afterwards, Dr. Julien would pass away once more due to old age, returning to the Departed Realm.

The Titanium Ninja
After Zane sacrificed himself to defeat the Golden Master with his Ice, Cryptor, Min-Droid, and most of the Nindroid army were destroyed, sending them to the Departed Realm.

Curseworld, Part II
After Nya killed the Preeminent with a tidal wave, the Cursed Realm was subsequently flooded and destroyed, causing all deceased Ghosts to be sent to the Departed Realm instead, which includes Morro, Chen, the Ghost Warriors, the Anacondrai Cultists, and Garmadon.

The Way Back
Seeking to reunite with Dilara, Nadakhan used one of his infinite wishes to bring her soul back from the Departed Realm, placing it inside of Nya's body. Later, when the Djinn was struck with the venom of the Tiger Widow, his power faded, causing Dilara to be sent back to the Departed Realm. After Nya was killed by the Tiger Widow venom, Jay used his last wish to reverse all events that had transpired since their escape from the hospital, thus erasing Nya's death and returning her soul from the Departed Realm.

Later, following the return of the Djinn Blade to Djinjago, its apparent destruction alongside its realm of origin would release the souls of Khanjikhan's predecessors and their enemies, sending them to rest in the Departed Realm instead.

Day of the Departed
On the Day of the Departed, Yang used the catalyzed magic of the Yin-Yang Eclipse to enhance the Yin Blade, tricking Cole into using its abilities to cut a rift from the Departed Realm to Ninjago for him to return. Using the Yin Blade's magic, Yang was able to bring back the souls of Samukai, Kozu, Cryptor, Chen, Morro, Eyezor, Zugu, four Stone Scouts, two Stone Swordsmen and multiple Nindroids from the Departed Realm, placing their spirits in statues modeled after their original bodies.

With the Yin Blade's magic only being able to keep the souls in Ninjago with the power of the Yin-Yang Eclipse, Yang instructed the resurrected villains to use the Departed Blades to switch places with their enemies, sending them back to the Departed Realm instead once the eclipse ended. Despite the efforts of the resurrected souls, however, all were killed by the ninja and sent back, with Morro in particular having instead made peace with himself and his former master before letting his soul go on unheeded to the Departed Realm.

Dread on Arrival
Harumi uses the three Oni Masks to create a portal to the Departed Realm in order to resurrect Lord Garmadon at the Temple of Resurrection, which was created out of the remains of the Royal Palace. From within the portal, the sounds of Garmadon's spirit becoming mortal can be heard. However, the Ninja were able to stop the ritual before its completion, closing the portal. Despite this however, the Ninja's efforts were in vain; Garmadon had returned to Ninjago after the temple was left abandoned and the Sons of Garmadon were arrested.

Two Lies, One Truth
Struggling with the good that remains within him, Lord Garmadon reveals to Harumi that his true motivation for reaching his True Potential is to defend Ninjago against a new darkness. During his time in the Departed Realm, he witnessed a frightening "everlasting night", and fears that it will threaten the world his father created as well.

Djinn/Sky Pirates
All the other Djinn are in the Departed Realm, except Nadakhan, who is the last survivor. He is currently imprisoned in the Teapot of Tyrahn.
 * Khanjikhan
 * Khanjikhan's Father
 * Dilara (spirit formerly resurrected through Nya by Nadakhan, now departed once more)

Cursed Ghosts
Many other ghosts are in the Departed Realm, sent there after the destruction of the Cursed Realm.
 * Morro, Master of Wind (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Chain Master Wrayth
 * Blade Master Bansha
 * Scythe Master Ghoultar
 * Bow Master Soul Archer
 * Ghost Ninja Attila
 * Ghost Ninja Hackler
 * Ghost Ninja Ming
 * Ghost Ninja Spyder
 * Ghost Ninja Howla
 * Ghost Ninja Wooo
 * Ghost Ninja Yokai
 * Ghost Warrior Cowler
 * Ghost Warrior Cyrus
 * Ghost Warrior Ghurka
 * Ghost Warrior Pitch
 * Ghost Warrior Wail

Anacondrai Cultists (Cursed)
All the Anacondrai Cultists are in the Departed Realm, except for Clouse, who is a ghost after escaping the Cursed Realm, and eventually got himself banished to the Underworld. Another associate of the Cultists, the Mechanic, is alive.
 * Master Chen (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Zugu (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Eyezor (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Chope
 * Kapau
 * Sleven
 * Krait

Nindroids
All the Season 3 Nindroids are in the Departed Realm, except some who are alive in Kryptarium Prison and some, who were reprogrammed and became Cyrus Borg's Security Droids. Three of them were resurrected during the Yin-Yang Eclipse, but they are now departed once more.
 * Cryptor (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Min-Droid
 * Mr. E

Stone Army

 * Kozu (formerly resurrected during the Yin-Yang Eclipse, now departed once more)
 * Stone Warriors
 * Stone Swordsmen (two were resurrected during the Yin-Yang Eclipse, now departed once more)
 * Stone Scouts (two were resurrected during the Yin-Yang Eclipse, now departed once more)

All the Stone Warriors are the Departed Realm except at least one or two Giant Stone Warriors, who may be the last survivors. One is currently in Kryptarium Prison, and the other one, if it isn't the same warrior, is trapped in a sinkhole under the Ninjago Museum of History.

Skulkin

 * Samukai (formerly resurrected during the Yin-Yang Eclipse, now departed once more)

Serpentine
All the other Anacondrai are in the Departed Realm, except for Pythor, who is the last survivor. His current whereabouts are unknown.
 * Arcturus
 * Anacondrai Generals
 * Anacondrai Serpent
 * The Great Devourer

Humans

 * Hiroshi
 * Dr. Julien (formerly resurrected by Samukai, now departed once more)
 * Captain Soto (formerly; resurrected by the Mega Weapon)
 * The rest of the Destiny's Bounty crew (formerly; resurrected by the Mega Weapon; one was disintegrated by the Mega Weapon and is now departed once more)
 * Nya (in an erased timeline)
 * Cliff Gordon
 * Emperor of Ninjago
 * Empress of Ninjago
 * Hutchins
 * Royal Guards
 * Cole's Mother
 * Harumi's Father
 * Harumi's Mother
 * Harumi
 * Many Elemental Masters
 * Many humans

Oni

 * Mistaké
 * Many oni

Dragons

 * Ultra Dragon
 * Fire Dragon (Flame)
 * Ice Dragon (Shard)
 * Earth Dragon (Rocky)
 * Lightning Dragon (Wisp)

Oni/Dragon Hybrids

 * First Spinjitzu Master

Oni/Dragon/Human Hybrids

 * Garmadon (formerly; resurrected by the Oni Masks)

Titans

 * Colossus

Animals/Creatures

 * Grundle (one formerly resurrected by the Mega Weapon, now departed once more)
 * Treehorn Queen
 * Many Animals

Trivia

 * If ghosts remain in Ninjago for too long without a vessel, they will begin to depart and will then be sent to the Departed Realm.
 * The Departed Realm has by far the most deceased souls of any realm.
 * Though the realm is populated by many people, in "Day of the Departed," the villains resurrected by Yang did not know each other.
 * It is the only realm in which the Realm Crystal cannot open a portal to.
 * Morro is the only villain who allied with the Ninja during the Yin-Yang Eclipse.
 * He was also the only one to willingly return to the realm after making his amends.
 * It is unknown if this realm will ever be visited. Though technically several characters have made it their place of permanent residence, off-screen.
 * It may be impossible for a being's spirit to ever truly die, as even "deceased" beings like cursed ghosts and skeletons go on to the Departed Realm if their bodies are destroyed (cursed ghosts formerly simply returned to the Cursed Realm, until it was destroyed).
 * It seems possible for beings inside the Departed Realm to return to the living world, as Garmadon stated he saw a terrifying darkness in his time there, later heavily implied to be the Oni, who were missing in their realm and thus may have died. However, how the Oni will resurrect themselves remains unknown.