Shadow Realm

The Shadow Realm was alleged to be a place of eternal suffering where people could be sent to, explicitly designed by 4Kids Entertainment for the dubbed version of the Yu-Gi-Oh! second series anime. When a death would occur in the Japanese version, it would usually be censored in the dub, sending the victim to the Shadow Realm instead. The concept is also mentioned in the Yu-Gi-Oh! GX anime.

Shadow Games were depicted as occurring in another dimension purported to be the Shadow Realm. It was this dark dimension (so named by Maximillion Pegasus) that formed the basis for the Shadow Realm in the English version.

When wagering a Duel in the Shadow Realm, summoning and maintaining a monster requires energy. The more monsters, the more energy it seems to require. In Yugi Muto and Pegasus's final Duel, Yami Yugi had to take over for the large portion because of the strain it had caused Yugi. In Joey Wheeler and Yami Marik's Duel, Joey would have won if he hadn't collapsed after the attack of "The Winged Dragon of Ra" took away the rest of his stamina.

Japanese version
The Shadow Realm as presented in the English language version of the anime does not exist in the Yu-Gi-Oh! manga and the Japanese version of the anime. However, the concept is based on an occasionally mentioned place called the World of Darkness (の Yami no Sekai). This was where the soul of Solomon Muto was placed after being absorbed into a "Soul Prison" card by Maximillion Pegasus.

In the Japanese version of ''Yu-Gi-Oh! GX'', Titan mentions that he was taken to the World of Darkness after losing to Jaden. Here, he met Kagemaru, who gave him his Shadow Charm mask, letting him return to Earth as one of the Shadow Riders. He Dueled Alexis Rhodes, one of the holders of the Spirit Keys, intending to defeat her and drag her to the World of Darkness, just as her brother previously had been. However, he lost to her and was dragged back there himself.

Purpose
The Shadow Realm was created to serve as a substitute for a character dying. Losing a Shadow Game, a fatal wound inflicted by a Duel Monster, the power of a Millennium Item, or any other mystical means would condemn their soul to the Shadow Realm instead of killing them. This was less permanent than killing the character, as it was established that it is possible to retrieve a soul from the Shadow Realm. In the dub of the Duelist Kingdom arc, Maximillion Pegasus was attempting to assemble all seven Millennium Items in the hope of restoring the body of his late wife, Cecelia, and rescuing her consciousness from the Shadow Realm. However, Cecelia appeared to have been sent to the Shadow Realm after dying from natural causes, rather than due to a Shadow Game or Millennium Item.

Replacements
The Shadow Realm is often criticized for censoring some of the darker aspects of the show, and for some of the more preposterous ways in which characters are banished there.

For example, in Yugi Muto and Arkana's Duel, the loser was to be sent to the Shadow Realm if touched by the "Dark Energy Disc". In the Japanese version, the disks were simply buzz saw blades that would dismember the loser's feet, presumably resulting in death from blood loss or shock.

Likewise, Yugi Muto and Seto Kaiba's had a Tag Duel against Lumis and Umbra atop a skyscraper in Domino City famous for its hollow interior, with each Duelist standing on top of a glass window rigged with a small explosive that would cause it to shatter upon losing. In the dub, the Duelist would fall into a portal to the Shadow Realm. In the Japanese version, the Duelist would simply fall to their death. This is why Umbra was prepared with a parachute, which he deployed when his window shattered, leaving his team-mate Lumis to surrender the Duel, before Marik Ishtar used the Millennium Rod to take control of his mind.

When Yami Marik banishes Mai Valentine's soul, her soul had been relocated to another plane in the Japanese version. In the dub, her soul was stated to have been sent to the Shadow Realm.

In the Battle City arc, after winning a Duel, Yami Bakura sent Bonz, Sid and Zygor to Hell in the Japanese version. In the dub, they were instead sent to the Shadow Realm.

Sometimes, the Shadow Realm can produce darker themes in the dub. Whenever a Rare Hunter lost a Duel to Yugi, Marik would take over their mind to talk to Yugi. Once finished, Marik would send them to the Shadow Realm without mercy, whereas in the Japanese version, the Rare Hunter would simply be knocked out. Some fans argue that being sent to the Shadow Realm is worse than being killed since the characters sent there are subjected to eternal torment rather than a peaceful "afterlife" when killed.

Tying the concept together towards the show's conclusion, Zorc Necrophades is credited with the creation of the Shadow Realm in the dub. Some characters are pulled out of the Shadow Realm in the dub of the anime and localized video games.

Known residents

 * PaniK: After losing to Yami Yugi in a duel, PaniK attempted to kill him, but the Millennium Puzzle shielded him and he banished PaniK to the Shadow Realm with a Mind Crush.
 * Ghost Kaiba: Sent there twice, once after Yami Yugi's and Seto Kaiba's Duel via Mind Crush, then again when he lost to Yami Yugi at Duelist Kingdom with another Mind Crush.
 * The Mugger: While threatening Téa, the mugger was challenged to a card draw game by Yami (who had taken over the unconscious Yugi Muto), who won and used a Mind Crush to banish the mugger's soul to the Shadow Realm.
 * Seeker: After losing to Yami Yugi in a Duel, Marik Ishtar used the Millennium Rod to take control of the Rare Hunter's body and trap his mind in the Shadow Realm.
 * Arkana: After losing to Yami Yugi in a Duel, Marik Ishtar used the Millennium Rod to take control of Arkana's body and trap his mind in the Shadow Realm.
 * Lumis: Once it was clear there was no way Lumis could win, Marik took over his body and trapped his soul in the Shadow Realm, as after Marik left him and he collapsed, Kaiba walked over to his lifeless form and picked up his locator cards.
 * Bonz: After being defeated by Yami Bakura in a Duel, Bakura trapped him in the Shadow Realm, along with Sid and Zygor. Presumably he never chose to release them.
 * Sid: After Yami Bakura defeated Bonz, he trapped Sid in the Shadow Realm along with him and Zygor. It is unknown if he ever released them.
 * Zygor: After Yami Bakura defeated Bonz, he trapped Zygor in the Shadow Realm along with him and Sid. It is unknown if he ever released them.
 * Mr. Ishtar: Who was sent to the Shadow Realm by Yami Marik with the Millennium Rod.
 * Mai Valentine: After Yami Marik defeated her in a Duel, he used his Millennium Rod to trap her soul in the Shadow Realm, which looked slightly similar to a Mind Crush in that the negative effect was used (but not the glass effect). She was later released when Yami Marik was destroyed.
 * Bakura Ryou: After Yami Bakura was beaten by Yami Marik, he vanished into the Shadow Realm, along with the original Marik's soul. However, Marik was still able to control Téa, and Yami Bakura hid inside Yugi's Millennium Puzzle (as he had placed a bit of his soul there in an earlier episode), thus the only one who was fully banished to the Shadow Realm was the original Bakura (however Yami Bakura's complete form and Marik's full form were still trapped there). He was later released when Yami Marik was destroyed.
 * Yami Bakura: After he was beaten by Yami Marik, he was sent to the Shadow Realm along with the real Marik, however, a portion of him still existed in the Millennium Puzzle. He returned when Marik undone all of Yami Marik's Penalty Games.
 * Marik Ishtar: After Yami Bakura was beaten by Yami Marik, he was sent to the Shadow Realm along with Yami Bakura and Bakura Ryou, however, a portion of him still existed in Téa's mind. Yami Marik then brought him back as he was going to use him as part of Yami Yugi's and Yami Marik's Shadow Game, where if Yami Marik lost Life Points, then Marik will lose parts of his body to the Shadow Realm. Later fully returned when he switched places with Yami Marik.
 * Mushara: While wandering through the tomb with Ahmet and Grandpa, he was slashed by a statue and fell into a pit of shadows, leading to the Shadow Realm.
 * Weevil Underwood: Temporarily sent to the Shadow Realm by Yami Bakura while along with Rex attempting to steal Yugi's Millennium Items (mistaking them for god cards).
 * Rex Raptor: Temporarily sent to the Shadow Realm by Yami Bakura while along with Weevil attempting to steal Yugi's Millennium Items (mistaking them for god cards).
 * Mokuba Kaiba: Temporarily sent to the Shadow Realm by Yami Bakura to make Kaiba Duel him.
 * Karim: Gave all his Ba to Shada so the "Two-Headed Jackal Warrior" could destroy "Giant Axe Mummy"; since his Ba was depleted, his soul was trapped in the Shadow Realm.
 * Aknadin/Shadow Magus: Destroyed by the "Blue-Eyes White Dragon", trapping his soul in the Shadow Realm.
 * Hassan: He jumped in front of the guards to protect them from Zorc's attack, causing his soul to go to the Shadow Realm.
 * Shada: His Ba was depleted when he jumped in front of the Pharaoh to protect him from Zorc's attack, causing his soul to go to the Shadow Realm.
 * Isis: Zorc destroyed her Winged Dragon Guardian of the Fortress, depleting her DiaDhankh energy and trapping her soul in the Shadow Realm as she fell.
 * Shimon: His Ba was depleted when his "Exodia the Forbidden One" was destroyed by Zorc, causing his soul to go to the Shadow Realm.
 * Priest Seto: His Ba was depleted when his "Blue-Eyes White Dragon" was destroyed by Zorc, causing his soul to go to the Shadow Realm. Was later released when Yami Bakura and Zorc were destroyed.
 * Yami Bakura's fragment: Was sent there when he lost a Shadow Game to Yugi Muto.
 * Titan: Sent to the Shadow Realm twice. The first time he was sent to the Shadow Realm after losing to Jaden, then again after losing to Alexis Rhodes.
 * Yami Marik: Sent there when the real Marik surrendered his Duel to Yami Yugi after regaining control of his body.

Duels that took place in the Shadow Realm

 * Yugi vs Pegasus (in the Duel in which Pegasus stole Grandpa's soul)
 * Yami Yugi vs Yami Bakura (in the Duel where Yugi, Joey, Téa, Tristan, and Bakura are all cards)
 * Yugi vs Pegasus (the finals of Duelist Kingdom)
 * Yami Bakura vs Bonz (in Battle City)
 * Mai vs Yami Marik (in Battle City)
 * Yami Bakura vs Yami Marik (during Battle City)
 * Joey Wheeler vs Yami Marik (in Battle City)
 * Yami Yugi vs Yami Marik (Battle City finals)
 * Seto Kaiba vs Yami Bakura
 * Lyman Banner vs Atticus Rhodes (off-screen)
 * Jaden Yuki vs Titan
 * Alexis Rhodes vs Titan

Trivia

 * The deaths of Gozaburo Kaiba, Noah Kaiba, the Big Five, Dartz, Shadi, Thief King Bakura, Yami Bakura, and Zorc were not censored with the Shadow Realm; however, Noah's death was censored by characters speculating that he saved his mind on a backup drive, and the Big Five's original deaths were temporarily censored by Noah imprisoning them in the virtual world, only to be destroyed along with it eight episodes later.
 * Also, PaniK's threats to incinerate Yugi, and Marik's Duel between Yugi and Joey that threatened to drown the loser, were not censored with threat of being sent to the Shadow Realm, unlike most other Duels that threatened death to the loser.
 * The Shadow Realm is often believed to be Hell, as they both have a similar concept of souls being condemned to eternal torment, and the Shadow Realm's creator, Zorc, appears to be the Yu-Gi-Oh! version of the devil. Indeed, the Shadow Realm is used as a stand-in for Hell as the final fate of Bonz, Sid, and Zygor.