Yami Yugi, known as Dark Yugi in the manga and Japanese versions, is the spirit of Pharaoh Atem that has been sealed in the Millennium Puzzle.
After Yugi Muto solved the Millennium Puzzle, Yami Yugi resided in Yugi's body and would take possession of it when Yugi or his friends were in danger. After Yugi became fully aware of Yami's existence, Yugi could voluntarily give control of his body to Yami.
In Super Smash Bros. Crossover, Yami Yugi is still a protagonist. He first appeared in Season 11 along with Jaden Yuki and Yusei Fudo to help Pichu and the Heroes of Legend fight Reiaz. Yami Yugi returns in Season 14 at the request of Marik from Yu-Gi-Oh Abridged to boost the series' ratings. Yami Yugi switches back to Yugi sometime after Pichu got the phone call from Psycho Kirby. Yami Yugi later gets visited within the Millenium Puzzle by Yami Bakura, who warns him there is a greater threat than Ganondorf. Yugi later switches to Yami Yugi before going to Fabia Sheen and Pandoria's battle. Yami Yugi later duels alongside Naruto Uzumaki against Infinity Mecha Sonic and wins. Shortly after, Yami Yugi, Naruto, and Goku begin the final battle against Pandoria. Yugi tells him beforehand that this is their last chance to save the world from Pandoria. Yami Yugi manages to avoid losing too many life points and helps deliver the finishing blow. In Season 15, Yami Yugi discusses the events of the previous season with Yugi when Jaden Yuki arrives to inform Yugi of Joey Wheeler's kidnapping. Yugi switches to Yami Yugi after arriving at the arena where Fabia fought against Pandoria. In Season 17, Yami Yugi is seperated from Yugi, and travels with Joey Wheeler until he gives the Millennium Puzzle to Naruto as he is about to be possessed by Nightshroud. Afterwards, Yami Yugi breaks down in tears at Joey being possessed by Nightshroud. Later, Yami Yugi reunites with Yugi as he, along with Naruto and Jaden, prepare to duel against Samus Aran with the fate of the world on the line. Yami Yugi is in control of Yugi's body for the remainder of the struggle against Yami Bakura. After Zorc is defeated again, Seto Kaiba declares Naruto and Sasuke Uchiha will duel him and Yugi to decide the champion of his tournament. Before the duel, Yami Yugi states that he looks foward to this duel. During Season 21, Yami Yugi is seperated from Yugi by Yami Bakura, and banishes Yami Bakura to the Shadow Realm after the Heroes of Legend defeat the malicious spirit. In Season 22, Yami Yugi duels alongside Jaden, Yusei, and Yuma Tsukumo against Yami Bakura to learn how to free Miles "Tails" Prower from his control. While the duel isn't seen, Yami Yugi is victorious, but is devastated to learn that to free Tails, they have to kill Infinity Titanium Mecha Sonic.
In the manga, Dark Yugi starts out as an unforgiving vigilante. He emerges to deal justice to people who trespass the souls of Yugi and his friends. Although his acts are righteous, his punishment Penalty Games are usually brutal. These are toned down in the first series anime, as most of them are made illusions. In the first episode of the English anime, Yami defeats Seto Kaiba and uses his power to break his mind. Kaiba is able to recover. He is slightly reserved, as he doesn't reveal his existence to Yugi or his friends. After Yugi admits to thinking "another Yugi" exists inside him, his friends become aware of his existence and accept him as a friend. Yami's pride is his greatest strength and weakness. Initially he refuses to lose games, without considering the consequences. This has caused him to almost kill Seto Kaiba by attacking him while he stood on a ledge and would fall if his monster was attacked and Yugi would have won the duel (in the Japanese version, Kaiba threatened to commit suicide should he lose). Yugi holds him back from such acts at times, although not always successful. Yugi becomes afraid to let Yami out for a while, because of the harm he could cause. During his duel with Rafael, Yami, albeit with great hesitation, eventually ignored Yugi's objections and used the Seal of Orichalcos rather than lose. Ironically, it was this action and Yami's subsequent corrupt actions during the duel would lead to one of his few defeats and the capture of Yugi's soul by Dartz. Yami expressed great grief and guilt following the battle due to Yugi's willingly suffering, which were because of Yami's actions. Learning how to lose becomes an essential part of Yami's journey, which he is tested in the Ceremonial Battle. Yami is also wise and intelligent. He knows all the rules and details of how the game is played. Yami is also capable of reading the ancient language of the Egyptians, figuring out the riddles or clues and what they mean. Through Yugi and his friends, Yami Yugi learns the values and powers of friendship and unity. After seeing Yugi overcome Marik in his Duel with Joey, who has been possessed, Yami thinks to himself, he learned something from Yugi; that in kindness lies the greatest strength of all; one day Yugi will surpass him in every way.
Yami Yugi's personality in Super Smash Bros. Crossover is unchanged from his personality in the second series anime.
Yugi's character design was overseen by Kazuki Takahashi.
As he exists in Yugi's body, his appearance is largely the same as Yugi's, although many alterations are made when Yami takes control. The main difference is that Yami Yugi looks more like a teenager than Yugi, is taller and has a deeper voice. In the Japanese version, though, very little change can be detected in Yugi and Yami Yugi's voice. His eyes are also narrower with a more intense, determined gaze.
Yami Yugi's hair features multiple layers including long blond crocked, pointy locks for his fringe. Unlike Yugi, some of the blond locks jut upwards. The rest of his hair features five large spikes colored black with magenta rims all along the edges. The spikes were loose and free flowing at the beginning of the manga, but over time became stiffer.
In many illustrations Yami Yugi is depicted having purple eyes like Yugi. But in some of the cover pictures of the Yu-Gi-Oh! R manga he is depicted having aqua green colored eyes.
At the beginning of the series, his outfit consists of the standard male Domino High uniform complete with a closed buckled collar and a set of Ankhs on his sleeves, which weren't present when Yugi was in control. It also noted that his uniform becomes a darker shade of blue when Yami Yugi assumes control. The Ankhs were later removed. Unlike Yugi, Yami Yugi sometimes wears the jacket as a cape.
He wears the Millennium Puzzle on a brown leather rope around his neck. The leather rope is later replaced with a chain.
When he played Dungeon Dice Monsters against Duke Devlin, he wears a dark-gray long-sleeved shirt, a sleeveless vest, dark blue pants and black shoes.
When he and Téa took a day together to find out about the Millennium Puzzle, he wore black linen and several pieces of wrist-chains, to match the Millennium Puzzle's chain.
In Yu-Gi-Oh! Capsule Monsters, Yami wears a different attire of a violet jacket and jeans. He also wears the Capsule Shooter on his left arm. In episode 4, he gains duel armor that allows him to become one with one of his capsule monsters.
In Super Smash Bros. Crossover, Yami Yugi uses his appearance from Battle City onward. During the final battle against Pandoria, Yami Yugi wears his jacket like a cape just like in Battle City. During the final battle with Samus, Yami Yugi removed the jacket.