The Light Brigade
The Light Brigade, known in Japan as the Four Monarchs (四帝, Yon Tei), is a group of assassin duelists in Sarina's service. All four Members decks are centered around a "Monarch". In addition, each member of the Light Brigade possesses some sort of element-based power. Frost, Thunder, T-bone and Blaze are shown to travel through snow, lightning, earth and fire, respectively; and the four seem to be responsible for using the Duel Spirits of the Monarch cards to create a spiritual barrier around Domino City.
The Light Brigade is introduced as Duel Academy students go on a field trip to Domino City. There, Frost and Thunder duel and kidnap Tyranno Hassleberry and Syrus Truesdale. T-Bone later duels Jaden Yuki and loses.