He appears to be the real Seto Kaiba and invited Yugi to duel him at the top floor of KaibaCorp. Yugi accepts and duels Kaiba. Mokuba interrupts the Duel partway through, telling Yugi that it isn't the real Kaiba, as Kaiba has not yet awoken from his catatonic state. The Kaiba that Yugi is playing against is actually a Cyber Kaiba, controlled by the KaibaCorp computer, using all of Kaiba's memories.
Cyber Kaiba plays a Giant Deck with "Automatic Giant" as his trump card. His other cards are all Equip Spell Cards that are used to power up "Automatic Giant" depending on what monster opposes him.