The Three Masked Knights 「仮面の三騎士 Kamen no Sankishi」 were a group of hungry students consisting of Harada (Slate in dub), Yamanaka, and Teraoka.
Coming across Marcel Bonaparte in the library, they were seduced by promises of power to join him in his cause. (In the dub, they were promised food from the food storage facility if they Dueled.) Through the magic of a "Polymerization" card, each of them was fused with a Duel Monster spirit which robbed them of their free will. The Three Masked Knights simultaneously DueledJesse Anderson, Axel Brodie, and Jim Crocodile Cook, serving as decoys while Marcel made his way to the area where the Sacred Beasts were sealed. They were returned to normal after being defeated.
Anger Mask (怒り仮面, Ikari Kamen), voiced by Kōichi Yokota and Eric Stuart, is a Duel Monster Spirit that was fused with Teraoka, an Obelisk Blue student. It Dueled Jim Crocodile Cook and released Teraoka upon being defeated.
Laughter Mask 「笑い仮面, Warai Kamen」, voiced by Daisuke Nakamura and Wayne Grayson, is a Duel Monster Spirit fused with Yamanaka, a Ra Yellow student. It Dueled Axel Brodie and left Yamanaka's body when it was defeated.
Emotionless Mask 「無表情仮面, Muhyōjō Kamen」, voiced by Yūki Fujiwara and Marc Diraison, is a Duel Monster Spirit that is fused with Slate (Harada in the original), an Obelisk Blue student. It Dueled Jesse Anderson and released Slate upon being defeated.