Yami Yugi and Seto Kaiba

Yami Yugi and Seto Kaiba have Dueled together as a tag team in the Yu-Gi-Oh! manga and anime. They have not fought together out of companionship, but usually to achieve a common goal or out of having no other option.

In Yu-Gi-Oh! World Championship 2008, the two are also part of a team, called Dueling Legends.

Manga
During the Battle City tournament, Dark Yugi was confronted by two Rare Hunters, who could not decide which of them should Duel first. Seto Kaiba, who had a strong dislike for Rare Hunters stepped in and insisted that they make it a Tag Duel. He told Dark Yugi not to get the wrong idea, he was not there to help him, but rather to "wipe out [the] card-counterfeiting scum". The Duel was quickly ended when Kaiba defeated the Hunters with "The God of the Obelisk".

As the Rare Hunters had difficulty defeating Dark Yugi and Kaiba, Marik Ishtar dispatched the Anti-God Attack Force, Mask of Light and Mask of Darkness. With Decks designed to work together and tailored to prevent the Summoning of Egyptian Gods, these Rare Hunters were more difficult for Dark Yugi and Kaiba to defeat, so more teamwork was required on their behalf.

Anime
Similar to the manga, Yami Yugi and Kaiba defeated the Rare Hunter Tag Teams, during Battle City.

When Kaiba confronted Dartz at the Paradius building, he challenged him to a Duel, but Yami felt it was too dangerous to face Dartz alone and suggested they Duel him together.