From that moment onwards, whenever Yugi or one of his friends is threatened by those with darkness in their hearts, this ' Dark Yugi ' shows himself and challenges them to dangerous ' Shadow Games ' which reveal the true nature of someone's heart.

As the series progresses and its focus shifts to the fictional card game known as Duel Monsters, Yugi and his friends learn that this other Yugi inside of his puzzle is actually the spirit of an unnamed Phaoroah from Egyptian times who had lost his memories.

As Yugi and friends attempt to help the Pharaoh regain his memories, they find themselves going through many trials and facing off against others wielding the mysterious Millenium Items.

The story takes place between the Battle City and Egypt arcs where Yugi and his friends must stop a man named Yako Tenma who plans to use Anzu Mazaki's body to revive Maximillion Pegasus.

His desire to defeat Yugi also grows from a grudge to an obsession, and Kaiba shows a disregard for the safety of Yugi and his friends.

Despite this, he still often helps them with defeating the villains they face, claiming that Yugi or one of his friends helped him and he owes them, or that the villain's desires are in direct conflict with his own interests.

He acquires the other three Blue-Eyes White Dragon cards in existence and builds " Death T ," a " theme park " made up of many deadly games and challenges designed to end the lives of Yugi and his friends.

After being subjected to the hazards, Yugi and his friends witness a Duel Monsters match between Seto and Yugi's grandfather, who was forced to participate when Kaiba threatens Yugi's life.

Meeting up with Yugi and his friends, Kaiba regains his deck and proceeds to Pegasus's castle.

Eventually, Kaiba teams up with Yugi to rescue Mokuba and Yugi's friends from Marik.

However, this was another attempt to do away with Kaiba, but Yugi and his friends manage to rescue him.

The craft taking the Battle City duelists to KaibaCorp Island for the finals is hijacked by Noah, who then traps Kaiba, Yugi and several of Yugi's friends in his own rendering of the virtual world, forcing them to duel the Big Five.

While Kaiba stops Gozaburo, a reformed Noah reprograms on of the satellites to attack the main computer database and helps Yugi and his friends escape.

This led to " Dark Yugi " being referred to as by Yugi's friends, and as by Yugi himself.

He becomes best friends with Yugi Mutou and the most important to him, who lessens his tough-guy exterior to reveal his true nature.

Anzu does not usually play games with Yugi and his friends, though she is once shown beating Jonouchi.

In the opening scenes of the 1999 film Yugi and his friends discover that she works at " Duel Monsters Center ," ( デュエル モンスター センター ), a Duel Monsters parlor.

During Duelist Kingdom, and later Battle City Tournaments, Anzu has several close encounters with the Shadow Games herself, including being turned into one of her favourite card monsters, the Magician of Faith ( when she and her friends became pawns of Dark Bakura as he and Dark Yugi dueled against each other in a Duel Monster Shadow Game ), and having her mind possessed by Marik, in his quest, or more precisely, plot of revenge against the Nameless Pharaoh ( a. k. a. Dark Yugi ).

Introduced as a new exchange student early on in the series, Bakura befriends Yugi Mutou and his friends and remains their friend for much of the series.

To accomplish this goal, he must defeat his arch-rival, the main protagonist of the series, Yugi Mutou, who has defeated him on several occasions.

Here, Kaiba is offered a deal – defeat Yugi in a duel in exchange for the right to duel Pegasus and save his sibling and company.

Even with this, Kaiba is once again on the cusp of defeat, until he places his own life on danger by balancing on the edge of the turret, forcing Yugi to forfeit the duel for fear of killing his opponent.

Encouraged by the vision, Yugi manages to defeat Kaiba and go on to the final battle against Marik.

Kaiba gives Yugi the card Fiend Sanctuary prior to the duel, and with it, Yugi is able to hold off the attacks of Marik's Winged Dragon of Ra and defeat him.

In the wake of his defeat at the Battle City Tournament, Seto began to suggest a means of defeating the three Egyptian God Cards that Yugi now holds, in order to defeat him and reclaim his title as world champion.

Yugi used this card to defeat Seto Kaiba in the Battle City semi-Finals.

She returns the favor by offering her extra star chips to Yugi following his defeat in his last duel with Kaiba.

Téa challenges Mai to a duel after Yugi refuses to respond to her kind gesture. Following Yugi ’ s defeat to Kaiba, she appears at the castle with enough star chips to qualify as a finalist.

After defeating Richard, Yugi suggests you defeat Rosenkreuz, and Crawford, who has now sided with the Lancastrians, reveals Seto is at the Stonehenge.

Desperate to defeat Yugi, Kaiba turns to Maximillion Pegasus, creator of Duel Monsters, to gain any new cards designed to defeat the God cards.

Kaiba departs promising to defeat Yugi, Yugi thanking Yami and his friends for their help and companionship.

He and Yami Yugi are able to give Stardust Dragon the power to defeat Sin Truth Dragon and defeat Paradox.

Later, during Battle City, Yugi acquires Dark Magician Girl, as well as his Magnet Warriors, Obnoxious Celtic Guardian, Buster Blader, Big Shield Guardna and Royal Knights, all of which become some of his most commonly-played cards.

Yugi, Honda Hiroto and Katsuya Jonouchi were beaten up by Kaiba's guards until the spirit of the Pharaoh Yami from within Yugi's Millennium Puzzle – beats up the guards and challenges Kaiba to a game of Duel Monsters with the card as a prize.

To avenge his grandfather, Yugi duels Kaiba and defeats him with Exodia, then uses his powers to purge the darkness that has clouded Kaiba's mind.

Pegasus captures Kaiba's soul, but when Yugi beats him in the final round of the tournament, the Kaiba brothers are both freed.

With Kaiba's aid, however, Yugi put the second mighty card into play – the Blue-Eyes Shining Dragon, able to destroy any card in play.

Yami, reunited with Yugi, destroys the Pyramid of Light card with the Blue-Eyes Shining Dragon and then uses Kaiba's planned strategy to summon the God Cards and end the duel by destroying Anubis.

Jaden is transported to the Game store 13 years in the past, and duels the high school aged Yugi that had just won the Domino City tournament.

During his duel with Jaden in the past, Yugi uses a slightly modified version of the deck he used during the Battle City tournament.

The former is used by Yugi in the final duel against Jaden Yuki, which occurs after Jaden is transported to the past, at a time before the cards were destroyed.

When Yugi and his friends witnessed these past events re-told as an interactive RPG-style Shadow Game, the thief's body was shown to turn to sand, but this was a metaphorical representation of Yami Bakura removing his " playing piece " from the " board " after it had served its purpose in the story, and not what truly happened to him.

Now, on his Graduation Day, Jaden is challenged by the present-day Yugi, who indirectly takes him to the past for a true Graduation Duel against a younger Yugi.