Overview
Here a quick guide how to obtain this achievement.
Deathbringer achievement
Deathbringer Achievement
This achievement can be found in the West coast, northwest of the City of light. This is a hidden area where you can walk over the background. Proceed north here and you will be teleported to the Ancient Cave. Equip the dagger you find there and use it’s ability.
Here some pictures, to help you figure.
Hope that will serve you.
Best regards,
Jack