The Master of Games is the main villain in the Teen Titans episode; Winner Take All.
The Master of Games transported Robin, Cyborg, and Beast Boy to his coliseum. He also transported the five other to participate in a tournament; Wildebeest, Speedy, Aqualad, Hotspot, and Gizmo. He told the eight contestants that the winner would become the Champion of champions. During the tournament, the Master had Cyborg fight Gizmo, with Cyborg winning the first round. Beast Boy fight Wildebeest, in which Wildebeest won. Aqualad fought Speedy, and Speedy won and Robin fought Hotspot, and Robin won.
After the first round ended, The Master told the winners that the loser returned home. However, The Master of Games was deceiving them. Anyone who loses the match gets aborbed by the Master Of Games's red gem and steals their powers. However, Cyborg couldn't shake the feeling that something was wrong. Cyborg eventually found out that the Master of Games plans, but the Master ended up absorbing him. The next morning, The Master informed that Cyborg was disqualified due to "sabotage". So he had them move to the final round; a three-way fight between Speedy, Wildebeest, and Robin. Wildebeest was the first to be defeated, which resulted in Robin and Speedy facing each other in a one-on-one fight. Robin emerged victorious, and Speedy was absorbed buy the Master of Games. When Robin returned to the coliseum, The Master revealed that he absorbed the loser, so he could be unstoppable. However, Robin played to the Master's ego, and asked him how could he be unstoppable if he didn't absorb the champion. The Master agreed to Robin's terms and decided to confront Robin in a one-on-one fight.
During the fight, Robin freed Cyborg and Speedy from the red gem. With the combine effort of Cyborg and Speedy, Robin was able to defeat the Master Of Games and freed the other heroes, and Gizmo from the red gem. After which, the Master of Games admitted defeat, and disappeared.
However, after Robin, Cyborg, Beast Boy, Aqualad, Hotspot, Wildebeest, Speedy and Gizmo returned home, the Master of Games somehow reappeared and transported eight female heroines and presumably their villainious counterparts including Raven, Starfire and Terra to his coliseum. It's unknown what happened during the tournament, though it's likely that the Master of Games was defeated after the tournament ended, and the heroines returned home.