He went insane thanks to the Dark One's counterstrike on saidin and attacked the city of Tzora. The city's Da'shain Aiel confronted him and tried to use their abilities of singing to restore him to sanity. Mondoran merely looked puzzled before putting all ten thousand of them to death. He subsequently destroyed the city, but the Da'shain's sacrifice bought an extra hour for the people of the city to flee. Mondoran then turned the entire city into a solid lake of glass. He is presumed killed in the chaos of the Breaking of the World.
Due to his apparent strength and severe madness in the early days of the Breaking, it is likely but unconfirmed that he was one of the Hundred Companions. Jaric and other mad male Aes Sedai (e.g. Haindar) likely did more damage than even Lews Therin Kinslayer since they targeted large cities. Despite this, most people in the present age blame the Dragon for the Breaking as he is seen to be more directly responsible for its initiation.