The Grass Sword Attacking Immortal Law was created by Violet Cloud Sect Master after he saw the Immortal Dao City.
Li Qiye traded it off from Violet Cloud Sect Master in the Ancient Heavenly Corpse Burial Ground.
Li Qiye gave it to Xu Pei to study, but he himself also learned it.
Long Jingxian copied it from Li Qiye after seeing him use it once against her. She wasn't able to grasp its true essence immediately though.
Links 1 Appearance(s) of Grass Sword Attacking Immortal Law