DC comics never really did much with AFOB. It is commonly thought that his powers came from exposure to the anti-gravity metal, Element 152, but this isn’t confirmed. His powers, of course, being the ability to take off his limbs and use them as melee weapons. And that’s all we know about him.
We (the audience) first meet Arm-Fall-Off-Boy when the Legionnaires first meet Arm-Fall-Off-Boy. As a hopeful prospect, AFOB is very excited to show off to the members.
AFOB has full confidence in his powers. He puts on a display, thinking he is impressing the Legionnaires.
However, to his great dismay, he is denied entry to the team. Thus the beginning of the greatest anti-hero to date. Look at the face in the last panel! That is the face of a vengeful vigilante, if I’ve ever seen one. Think about this, outcast by the superhero team he had dreamt of being a part of, for as long as he could remember, Arm-Fall-Off-Boy, now a crushed spirit, loses trust and faith in all heroes. Now, with a distaste for heroes, AFOB fights crime in his own way, and isn’t afraid to take on a “good guy” once in awhile if they dare get in his way.
Forget Punisher, forget Deadpool, forget Batman, forget whoever else you may think of, Arm-Fall-Off-Boy is the new greatest hardcore vigilante. With the new imprint DC Black Label, a comic with a guy using his arm as a bat to beat someone senseless is a total possibility.