Departed Realm

 The Departed Realm is one of the Sixteen Realms. The dimension is where beings from all known realms, including the Cursed Realm, Ninjago, and the Underworld, go to after they die.

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, 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 killed by the overwhelming power and sent back to the Departed Realm once again.

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

Curse World - 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.

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. 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 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, with Morro in particular having instead made peace with himself and letting his soul return unheeded to the Departed Realm.

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 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 Warrior Cowler
 * Ghost Warrior Cyrus
 * Ghost Warrior Ghurka
 * Ghost Warrior Pitch
 * Ghost Warrior Wail
 * Yokai

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 in Kryptarium Prison.
 * 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 (Overlord Faction)
All the destroyed Nindroids are in the Departed Realm, except some who are alive in Kryptarium Prison. 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

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 Giant Stone Warrior, who may be the last survivor. He is currently in Kryptarium Prison.

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

Humans

 * The First Spinjitzu Master
 * Dr. Julien (formerly resurrected by Samukai, now departed once more)
 * Garmadon
 * Captain Soto (formerly; resurrected by the Mega Weapon)
 * The rest of the Destiny's Bounty crew (formerly; resurrected by the Mega Weapon)
 * Nya (In an alternate timeline)
 * Many Elemental Masters
 * Many humans
 * Cliff Gordon (In an alternate timeline)

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.
 * Morro is the only villain who allied with the Ninja during the Yin-Yang Eclipse.