That thing the Joker bought from Riddler was the same liquid that made Joker
- In this case, the person Joker was threatening to kill would be Harvey Dent, leaving nothing but a psychopath like Harvey's worse half in control.
The Riddler sold the Joker stolen technology for making artificial life
- The Joker had figured out a way to use this technology to kill Harvey's worse half. The reason Two-Face knows a man that can "make everything in that case disappear" is because the Riddler stole it from Lex Luthor, who got it in Azzarello's other comic about a famous DC comics villain.
Johnny Frost survives
The story seems to be a retrospective account. While it was a realistic take on the mythos,it wasn't that realistic.