he was extremely smart, he had great control, benefited from an expanded strike zone
i think it was in an interview on lebatards show where he said by the end of his career he could literally hit the catchers glove without it moving 9/10 times
cool story about maddux from the padres broadcast crew:"Maddux would have relatively highly attended bullpen sessions between starts. A number of fans would come early to certain games just to watch him throw a bullpen. During these bullpens, sometimes someone in the bullpen would throw a towel over the catchers mask to put on a show for the fans. The bullpen coach would give the catcher a heads up when the ball was about halfway to the plate so he can catch it. Maddux would hit the catcher's mitt every time."