The Gunstringer

To get this achievement, you first need to unlock hardcore mode in the Bonus Store from the Main Menu. I believe it costs $14,700. After doing this, you need to play an ACT. The Prologue will NOT work. I did it on the Gatorjack level (Act 2, New Orleans area) because it is the shortest level I believe outside of the Prologue.

Before starting the level, you'll be asked to select modifiers, commentary (if you've also bought that), and hardcore mode. Select hardcore mode, but something that can make it easier is that if you also unlock the "No Fail" modifier, which I believe also costs $14,700, you can combine them and still get the achievement because I got this at the same time as the "Why Would You Even Do This?" achievement with all the modifiers activated. I believe all modes/modifiers cost $14,700 , but if you're played through a few acts, you should have plenty of cash to combine the achievements if you so choose.