Over in Howard Bagby's discussion "A Batman A Day", I mentioned that after Denny O'Neil became editor of the Batman titles, we saw the beginning of the overexposure of the Joker. O'Neil became the editor with Batman 401 and Detective 568, cover dated November 1986. In addition to a number of appearances in each title over the next few years, the Joker was featured in The Dark Knight Returns, The…