Originally Posted by Redonkulous BP
Also, it is not based on the number of shots you use throughout the game. It is situation specific. For example, if you do not shoot concrete blocks on the lasers on Wily's last level, you can not use those elsewhere - it will void the achievement.
What do you mean by situation specific? In the Wily 2 area where you're supposed to jump through a phantom block I actually used two concrete shots because I fucked up the first time. I got the achievement on that run though. I was thinking maybe it's because I used spike guards to get across the section in Wily 1 where you're supposed to use Rush Jet, so it made up for my mistake.