When Yugi Muto solved the Millennium Puzzle, he was infused with the ancient spirit of Yami Yugi. Yami Yugi is ready to face any challenge in order to regain his lost memories. An expert Duelist wielding unmatched skills and cards, Yami Yugi's most trusted monster is "Dark Magician."
When Yu-Gi-Oh! Duel Links is started after it is successfully downloaded in its entirety, Kaiba will appear, being prepared to defeat Yami Yugi in a Duel. Yugi will mutter "Kaiba..." before declaring that he cannot afford to lose. Depending on the player's choice, either he or Seto Kaiba can then be utilized in the subsequent tutorial Duel.
After Kaiba concludes his global announcement in Duel World, if the player had previously chosen Yami Yugi as their initial character, Yami Yugi will appear in Duel World at this point; otherwise, he will only appear after the player reaches Stage 15. In either case, he notes that "this is the new venue for Dueling..." and thus the place to determine who will be the Duel World King. He then asserts to the player that he never runs from a challenge, before declaring that he will compete with all of his strength to prove that he is a true Duelist. (Yugi's dialogue ends at this point, unless the player had chosen Yugi as their initial character, in which case Yugi also declares that he'll compete alongside his 'dear friend': "Dark Magician".)
Seto Kaiba route
If the player chooses Seto Kaiba as their initial character in Yu-Gi-Oh! Duel Links, they will also encounter the following instances of unique dialogue, as they attempt to unlock Yami Yugi as a playable character.
Until the player has already defeated Yami Yugi at least once in a non-tutorial Duel, whenever they challenge him to a Duel, Yugi will realize that he himself is the "boss" of Stage 15. He then declares that a Duelist must always fight with his heart, so he will not go easy on the player. He also adds that if the player is a true Duelist, he expects nothing more than their best strategies.
Until the player has already defeated Yami Yugi at least once in a non-tutorial Duel, whenever they lose to him, the latter will state that it's clear the player has much to learn. He then reminds the player to believe in the heart of the cards, as it will never mislead the player, and that he looks forward to his next Duel with the player.
When Yami Yugi loses to the player for the first time (in a non-tutorial Duel), he congratulates the player and acknowledges that they defeated him. He then states the player can now proceed further ahead, but also promises that he'll catch up so he can Duel the player again. At that time, he concludes, the both of them should create an incredible Duel for the ages.
When the player claims their final unclaimed reward for Yami Yugi's Character Unlock Missions, they will encounter Yami Yugi again, who reveals that the reason he keeps Dueling is because there's something waiting for him at the end of the road, although he admits he does not know what that "something" is. However, he proclaims that a true Duelist keeps fighting to find the answer, and says that his friend will help him: "Dark Magician".
Draw Phase, instead of doing a normal draw, draw a random Spell/Trap card.
Can be used each time your Life Points decrease by 1800. In the Draw Phase, instead of doing a normal draw, draw a random Spellcaster-Type monster.
Can be used each time your Life Points decrease by 2000. In the Draw Phase, instead of doing a normal draw, draw the card of your choice.
Whenever Yami Yugi Summons "Dark Magician", a cut-in frame of Yami Yugi will briefly appear, and he'll announce "My ever-faithful companion, Dark Magician!" If that player hasn't already Summoned "Dark Magician" during that Duel, a cutscene of "Dark Magician" being Summoned will play afterwards.
Most of the time when he declares an attack with that monster, he announces "Go, Dark Magician!" followed by "Dark Magic Attack!"
Whenever Yami Yugi Summons "Dark Magician Girl", a cut-in frame of his face will briefly appear, and he'll announce "The great Dark Magician has a disciple who can more than hold her own!" followed by "Say hello to Dark Magician Girl!"
Most of the time when he declares an attack with that monster, he announces "Go, Dark Magician Girl!" followed by "Dark Burning Attack!"
Whenever Yami Yugi activates "Polymerization", he announces "It's time for me to use a Spell Card." This is followed by "I activate Polymerization!"
Whenever Yami Yugi activates "Thousand Knives", he announces "The Spell Card, Thousand Knives!"
Whenever Yami Yugi activates "Mystic Box", he announces "I activate my Spell - Mystic Box!"