The Chess event in Karazhan must be solved in order to reach Prince Malchezaar. The raid plays a sort of chess match against Medivh. Although the analogy to chess is usable (Doomguards are "stronger" than Footmen for example), it's not very strict. The pieces from the event behave very differently from real chess pieces, in particular player-controlled pieces autoattack enemy pieces they face, and the Kings are actually the strongest pieces in the game. In order to start the event, a player has to talk to the King piece of their own faction. The objective is to kill the enemy King without losing one's own King. If the game is won, a Dust Covered Chest appears with loot. Many players see this encounter as an easy fight, referring to it as "the free epics".