(I grew up watching the 60's series with Caesar Romero) It's been decades but I can still remember the depiction of the shadows on the wall of the Joker, holding a crowbar standing over robin with 'HA HA HA HA HA HA!' all over the page. It was the first time that I remember seeing the joker as the horrid piece of malevolent garbage that he really is, instead of some thug who had a trademark ever-present grin. The story inside was equally shocking and I remember really, really enjoying it. I remember the cover of the comic 'A Death in the Family' and how shocking the depiction of Batman holding Robin's broken body was to me at the time I first saw it.
