Box art - Anarchy Reigns

Anarchy Reigns Anarchy’s Executioner Achievement Trophy Guide

In order to unlock Anarchy's Executioner, you have to defeat every boss with your Killer Weapon. It doesn't matter if you use a weak or strong attack, just so long as your holding the right trigger to activate your "Killer Weapon." You'll not you got it when you get an Overkill! +10000 bonus with your final hit.