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 English version to say he/she is sent instead to "Shadow Realm". The concept is also mentioned in the Yu-Gi-Oh! GX anime.
The Shadow Realm as presented in the English-language version of the anime does not exist in either the original Japanese-language Yu-Gi-Oh! manga or anime series. However, the concept is based on an occasionally mentioned place called the World of Darkness (Yami no Sekai). This was where the soul of Solomon Muto was placed after being absorbed into a "Soul Prison" card by Maximillion Pegasus. This World of Darkness was also mentioned by Titan in the Japanese version of Yu-Gi-Oh! GX. He was taken there 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 would Duel Alexis Rhodes, one of the holders of the Spirit Keys. His intent was defeat her drag her to the World of Darkness, just as her brother had previously been. However, he would lose to her and be dragged back to the world himself.
The 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 was to form the basis for the English-language Shadow Realm, and as mentioned above, it was essentially created to serve as a substitute for death, or characters dying. The loss of a Shadow Game, a fatal wound inflicted by a Duel Monster, the power of a Millennium Item, or any other mystical means will, rather than outright kill a character, condemn their soul to the Shadow Realm - "a softer defeat" in essence, as it is established that a soul could be extracted from the Shadow Realm if need be. Indeed, this was the entire basis for the storyline of the dubbed version of Duelist Kingdom, where Maximillion Pegasus was hoping 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. It is unclear if the souls or consciousness of a person is sent to the Shadow Realm if someone were to die from natural causes, as appears to be the case with Cecelia.
The very concept of the Shadow Realm is often derided, mostly for the basic fact that it is a result of the censorship of some of the darker aspects of the show, but it is also partly because of some of the more preposterous insertions of the Shadow Realm. Many of the dubbed show's fans also believe that although souls can be "retrieved" from the Realm and given back to characters, unlike when dead, that this is worse in the long run, since being banished to this eternal darkness is similar to forever living in a place like Hell instead of the peaceful "afterlife" when killed in the original.
An example of the unreasonable insertions is when facing the conjurer Arkana, Yugi Muto comes under threat from a "Dark Energy Disc" which, if it touched him, would send his mind to the Shadow Realm. In the Japanese version, the disks were simply buzz saw blades that would dismember the loser's feet, probably resulting in death.
Similarly, the Shadow Realm was used during a tag-team Duel that involved Yugi Muto and Seto Kaiba Dueling Lumis and Umbra atop a skyscraper in Domino City, famous for its hollow interior. In the English-language version, the windows they stood on has a small explosive device on them, which would cause a small explosion, resulting in the glass shattering when each Duelist lost, dropping them into a "portal", which would then transport the unfortunate victim to the the Shadow Realm. In the Japanese-language version, the windows shatter as they do in the Dub, but here, the Duelist would simply fall to their death, falling all the way to the floor. This can be further evidenced by Umbra being prepared with a parachute, which he deployed when his window shattered, after he lost all of his Life Points, leaving his team-mate Lumis to surrender the Duel, and eventually has his mind taken over by Marik Ishtar and his Millennium Rod.
Conversely, on occasion, the idea intersects with some of the original visuals - for instance, when Yami Marik does away with Mai Valentine's soul, visuals distinctly show her soul to have been relocated to another plane, which the English-language version is then able to refer to as the Shadow Realm.
Also, it sometimes actually causes the show to create darker aspects - when the Rare Hunters dueling Yugi (and Kaiba in their Tag-Team Duel) fail, Marik takes over their minds and after chatting with Yugi in both versions, he angrily sends them to the Shadow Realm in the dub, instead of just making them lose consciousness for a short time (and not die) in the original.
Tying the concept together towards the show's conclusion, the demon, Zorc Necrophades, is credited with the creation of the Shadow Realm in the English-language version. Some characters are pulled out of the Shadow Realm in the English anime and the English-language video games.
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 and Pegasus's final duel, Yami had to take over for the large portion because of the strain it had caused on little Yugi. In Joey and Yami Marik's duel, Joey would have won if he hadn't collapsed after the Winged Dragon of Ra's attack taking away the rest of his energy and strength.
The Shadow Realm is similar to (and probably based on) the religious concept of Hell.
- PaniK: After Yami Yugi beat PaniK 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.
- 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 the Rare Hunter: After losing to Yami Yugi in a Duel, Marik 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 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 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. However as Mokuba, Rex and Weevil came back after they were sent there by Bakura its possible that they were released, and Bakura's death could have released 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.
- Ryo Bakura: 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 truly banished to the Shadow Realm was the original Bakura. He was later released when Yami Marik was destroyed.
- 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).But he later released.
- 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).But he later released.
- Mokuba Kaiba: Temporarily sent to the Shadow Realm by Yami Bakura to make Kaiba Duel him.
- Karim: Gave all his diadankh energy to Shada so the Twin-Headed Jackal could destroy Giant Axe Mummy, and since his diadankh was depleted, his soul was trapped in the Shadow Realm. Was later released when Yami Bakura and Zorc were destroyed.
- Aknadin/Shadow Magus: Destroyed by the Blue Eyes White Dragon, trapping his soul in the Shadow Realm. Was later released when Yami Bakura and Zorc were destroyed.
- Hassan: His diadankh energy was depleted when he jumped in front of the guards to protect them from Zorc's attack, causing his soul to go to the Shadow Realm. Was later released when Yami Bakura and Zorc were destroyed.
- Shada: His diadankh energy 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. Was later released when Yami Bakura and Zorc were destroyed.
- Isis: Zorc destroyed her Winged Dragon Guardian of the Fortress, depleting her diadankh energy and trapping her soul in the Shadow Realm as she fell. Was later released when Yami Bakura and Zorc were destroyed.
- Shimon: His diadankh energy was depleted when his Exodia was destroyed by Zorc, causing his soul to go to the Shadow Realm. Was later released when Yami Bakura and Zorc were destroyed.
- Priest Seto: His diadankh energy 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.
- 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.
- Solomon Muto: Pegasus trapped his soul inside a card, and could have possibly been the Shadow Realm, or similar to it. Pegasus later released him after his defeat by Yugi.
- Mokuba Kaiba: Pegasus trapped his soul inside a card, and could have possibly been the Shadow Realm. Pegasus later released him after his defeat by Yugi.
- Seto Kaiba: Pegasus trapped his soul inside a card, and could have possibly been the Shadow Realm. Pegasus later released him after his defeat by Yugi.
- Umbra: In the Duel against Yugi and Kaiba, Kaiba Summoned Obelisk the Tormentor and took out all of Umbra's life points, causing the "shadow barrier" glass to break and causing him to fall into the Shadow Realm. Though he activated a parachute, his mind appears to have been trapped to the Shadow Realm, as he was quite motionless. However, it is debatable that he may have "stopped the effect" in time when the parachute caught on a pole. Whether or not he was truly sent to the Shadow Realm remains unknown.
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