I agree with the assessment that the villains that Batman faces in The Dark Knight Returns are reflections of himself.
Harvey Dent/ Two Face is the most obvious. It is clear that Bruce Wayne/ Batman sees Dent as a mirror of himself. Dent, a former District Attorney and hero is deformed and turned into a criminal at the hands of criminals. Dent is of two minds as well as two faces: The hero and the criminal. He cannot decide between these two, and so uses a coin to make decisions. When we first meet Dent he has been “cured” physically and mentally. He tries to return to society as a normal man, reformed, but as we discover he is incapable of remaining this way and his true divided nature reemerges. Wayne follows a similar trajectory. After the death of the second Robin, Jason Todd, Wayne has retired from being Batman and tried to return to normal society. He even sponsors Dent rehabilitation because he needs to believe that people’s “private demons can be defeated” (17). Both men finally succumb to their private demons and Batman must defeat Two Face. In this confrontation, Batman acknowledges that they are mirror images when he says he sees a reflection.
Less obvious reflections of Batman are the other enemies he confronts. Batman is a character of many divisions. The conflict between these divisions is reflected in Dent, but the divisions themselves take the form of the others that Batman faces off against. Batman squares off against the Mutant gang leader. The Mutant Leader represents raw brute force and criminality. Batman walks the line between law enforcement and criminal. To defeat the Mutant Leader, Batman must circumvent the law and defeat the leader at his own game. The Mutant Leader is the reflection of Batman’s criminality and barbarism.
The Joker is a distorted reflection. Joker is in many ways the opposite of Batman. While Batman seeks a kind of fascistic control over the criminal element in the city, the Joker is the anarchistic soul of crime. He is a villain and a murderer, but by defeating him, Batman has become a villain and murderer in the eyes of the public.
Finally, Batman must square off against Superman, the hero. In this confrontation, Batman must face the publicly accepted superhero as the public villain. In defeating Superman, he must himself be defeated. He beats Superman, but it costs him his life.