Battle Royal

A Battle Royal (バトル・ロイヤル) is a special kind of duel involving 3 people.

On the anime, this is to be understood as a triangle duel. It applies the rules of a normal Duel, however since there's an extra player on the field, it adds the choice for 2 players to cooperate against the other player. This type of duel has only been mentioned to be carried out twice on the anime series.

Yu-Gi-Oh! GX
The first time this kind of duel was aplied on episode 175. At the time when Yusuke Fujiwara dueled like this while trying to defeat Jaden Yuki and Jesse Anderson.

Yu-Gi-Oh! 5D's
On episode 106 this type of duel is to be used by Yusei Fudo and the others, all while trying to stop the army of Ghost's.