My take on the villians is this. If you have seen the movie Unbreakable. You know that Sam Jackson's character says there are always two villains.
One is the Soldier Villian and the other is the Brain villian. So in BB Ra's is the brains. The Scarecrow is the Solidier. In TDK Joker is the brains, 2face is the villain.
So if you want to know which villians fit into plots look at the characters.
Penguin is going to be Brains. Riddler is going to be brains, Catwoman/Freeze/Poison Ivy are going to be soldier villains.
GS
One is the Soldier Villian and the other is the Brain villian. So in BB Ra's is the brains. The Scarecrow is the Solidier. In TDK Joker is the brains, 2face is the villain.
So if you want to know which villians fit into plots look at the characters.
Penguin is going to be Brains. Riddler is going to be brains, Catwoman/Freeze/Poison Ivy are going to be soldier villains.
GS