The Duel Giant is how Brier and Beauregard are called while they are dueling along side each other, Beauregard playing the part of the Duelist, and Brier giving him instructions via a radio headset. Brier is extremely shy, so, while Beauregard Dueled in his place, he could show all his potential, and Beauregard wanted to Duel during the night so that other people wouldn't be afraid of his large size. By this way, the both of them created the "Duel Giant", forcing other Obelisk Blue students to Duel against them using forbidden rules. However, after Dr. Crowler sends Jaden Yuki to defeat them, the latest convinced them to battle him out in the open in exchange for not turning them in.
As the Duel Giant, Brier and Beauregard use a Goblin Deck, which includes high-ATK strength creatures such as "Giant Orc" that can have its drawback removed by the Union Monster "Second Goblin". This deck was likely chosen in that the Giant Orc and Second Goblin function much like Beauregard and Brier themselves.