Do you want to compare John Grey with Callisto? Discover the powers, weakness & weapons of John Grey and Callisto from John Grey Biography and Callisto Biography. Find out all about John Grey and Callisto.# Check out how is John Grey unique and distinct from Callisto. Discover their love interest, sidekicks, family tree and the movies and games list in which John Grey and Callisto have appeared. Find out everything about them here!