BS says a toad transformed into an angel.
Benjamin Saunders, in William H. Kelley, "Miscellany," circa September 1884, in Dan Vogel, Early Mormon Documents (Salt Lake City, UT: Signature Books, 1998), 2:137.
I heard from <Joe> tell my Mother and Sister how he procured the plates. He said he was directed by an angel where it was. He went in the night to get the plates. When he took the plates there was something down near the box that looked like a toad that rose up into a man which forbid him to take the plates.