Devil appeared as an angel

1. Alma 30: 53
     53 But behold, the devil hath deceived me; for he appeared unto me in the form of an angel, and said unto me: Go and reclaim this people, for they have all gone astray after an unknown God. And he said unto me: There is no God; yea, and he taught me that which I should say. And I have taught his words; and I taught them because they were pleasing unto the carnal mind; and I taught them, even until I had much success, insomuch that I verily believed that they were true; and for this cause I withstood the truth, even until I have brought this great curse upon me.
2. D&C 128: 20
     20 And again, what do we hear? Glad tidings from Cumorah! Moroni, an angel from heaven, declaring the fulfilment of the prophets—the book to be revealed. A voice of the Lord in the wilderness of Fayette, Seneca county, declaring the three witnesses to bear record of the book! The voice of Michael on the banks of the Susquehanna, detecting the devil when he appeared as an angel of light! The voice of Peter, James, and John in the wilderness between Harmony, Susquehanna county, and Colesville, Broome county, on the Susquehanna river, declaring themselves as possessing the keys of the kingdom, and of the dispensation of the fulness of times!