The Designer sounds like an ultra planner. I like the explanation of how he would help the villains outwit Batman: by going 10 levels ahead of their normal heists and crimes. Of course, having the Designer chat with the Joker at length would ruin a good thing. The Designer suddenly became violent and tried to kill all four of Batman’s villains.
As Catwoman described the encounter between the Designer and the Joker:
Imagine being the first one to understand what that monster was going to become. Imagine going step-by-step from diamond magnates to Joker fish to gassing entire buildings to murdering countless families. It must have been like starring into the abyss, Bruce. realizing that this strange crime boss with clown makeup would keep going and adapting until he became something apocalyptic.
From – Batman Vol. 3 #90
I get they are trying to do another Jokes and Riddles to explain some characters and their growth, but The Designer sounds like fanfic material. He really does. Frankly I just imagine that the Joker was always like that. There was no PG Silver Age Joker to start with. He just always was a complete monster. He just escalated on his own accord.