I Am The Hero

This achievement will unlock when you use Critical Attack 100 times. You use it by pressing punch while an enemy is about to hit you. Do not press any direction or it will not work. It is easier when there are some enemies at the same place and you keep pressing punch. I got all 100 without really trying in my first playthrough. But if you want to get them early I found the guys with the boxing glove gun easiest to time.