- Ass Pull: How exactly the Joker scammed Mxy out of his "secret imp name" is glossed over, to say nothing of how he (a largely Gotham-bound criminal whose interactions with Superman's wheelhouse are occasional at best) would even know about such a mechanic in the first place. Indeed, the very idea of fifth-dimensional imps having this weakness was something never even implied before (or since) to readers.note
- Crosses the Line Twice: The whole storyline is chock full of these moments. One of the best is probably the Joker playing poker with the corpses of all three (at the time) Robins.
- Harsher in Hindsight: Late in the story Joker tries to break Superman by getting him to accidentally kill all his friends and loved ones, attempting to push Superman to the point of wanting to kill him in retaliation. While he fails here, over a decade later we would see what would happen when Joker pulled a similar tactic and it did break Superman enough to kill the Joker, with the end results as messy as you think.
YMMV / Emperor Joker