In 19-20th episode of Tribes and Empires, Mr. Mo tells Muyun De why he has to kill Huang Xuan‘s role Muyun Sheng after forcing the leader of Longyuan pavilion to tell him the truth of Muyun pearl via soul returning magical arts.
As Longyuan pavilion’s leader doesn’t want to tell Mr. Mo the Muyun pearl’s secret and commits sucide, Mr. Mo uses soul returning magical arts and gets the secret.
He persuades Muyun De to return the pearl, but Muyun De refuses it and claims he will destroy it if he cannot keep it.
Mr. Mo warns to kill him if Muyun De doesn’t follow his suggestion. Muyun De asks what his teacher looks for. Mr. Mo says that it’s glory and reveals Muyun pearl can turn Muyun Sheng into God, so that he can kill the God and become the one of Novoland. which is the goal of their Chen Yue Sect in the past 1000 years.