Twenty years prior to the series , Leanbow led the other Mystics in the Great Battle against the Supreme Master of the Underworld .
His Forces of Darkness led by Morticon in order to prevent them entering the human realm .
Twenty years prior to the series , Leanbow led the other Mystics in the Great Battle against the Supreme Master of the Underworld , and his Forces of Darkness led by Morticon in order to prevent them entering the human realm .