You astrally leave your body and become that of another form, either by shifting the appearance of the spirit, or entering the body of another being on this plane (this too is included in the Walk-In?
section, and overlaps with that of the shapestealer definition below).
An Astral Shift occurs when a lycanthrope enters a spiritual trance, travels out of body to the astral plane, and shifts there. Sometimes, it's hard to tell the difference between Lucid Dream Shifts and Astral Shifts, lucid dreams being just as real, but Astral Shifts are sometimes associated with "psychic" experinces as well, such as : dream sharing, telepathy, clairovoyance, precognition, and psychokinesis. Astral Shifts are also said to be more spiritual in nature.