Lumis and Umbra are tag-team members of Marik Ishtar's Rare Hunter organization. They pride themselves on being an unbeatable tag team.
Lumis (Mask of Light in the manga and Japanese anime) is the short and thick one with the white-colored, smiling mask on the right side of his face, as pictured on right. Despite his size, he is very acrobatic, and managed to jump to a skyscraper through lower rooftops. In the manga, he tends to say "Got it?" to end his sentences, and dislikes being called "shrimp".
Umbra (Mask of Darkness in the manga and Japanese anime) is the tall and thin one with the black-colored, frowning mask on the left side of his face, as pictured on left.
In the anime, they have receivers attached to their masks, so they can secretly communicate their strategies with one another. This was not shown in the manga.
After Marik's goons successfully capture Joey, Mokuba, and Téa (in the manga, the Mask of Light used a Duelist Chastity Belt to lock Kaiba's Duel Disk, with the key to it being the hostage), both duelists (now wearing their half-masks) challenge Seto Kaiba and Yugi Muto to a Tag-Team Duel at the rooftop of a skyscraper. In this duel, the glass panels that they are standing on each have a Shadow Box attached to them. As soon as a player's Life Points drop to 0, the Shadow Box will go off sending the loser falling and trapping them in the Shadow Realm before the fall (for the Japanese version, the Shadow Boxes were bombs that would detonate, sending the loser to fall through a 130-foot building to his death).
Despite the advantages Lumis and Umbra had, after a slip up made by Lumis, and with some provoking from Kaiba, the masked duo's teamwork faltered, which led to their eventual defeat. Seto Kaiba managed to use "Soul Exchange" to summon Obelisk the Tormentor and used it to defeat Umbra, sending him down the window pane (Umbra had a parachute waiting although it is possible that in the English anime his soul was trapped in the Shadow Realm anyway). Lumis surrenders and Marik uses him to communicate with Yugi, presumably trapping his soul in the Shadow Realm with his Millennium Rod.
Umbra and Lumis play Mask-themed Lockdown Decks, that weaken and manipulate the opponent's cards while lowering their opponent's Life Points. Umbra plays a Deck with more Monster Cards while Lumis uses more Magic and Trap cards. They also rely on teamwork to support each other, while taking down the opponents. When provoked by Kaiba, coupled with several slip-ups, their teamwork faltered, leading them to defeat.