Middle-earth: Shadow of Mordor - Game of the Year Edition

Pretty straightforward. As you advance through the game, you should have the opportunity to unlock the "Death Threat" upgrade. This allows you to press Y to issue a death threat to captains through the domination of a subservient orc.

When the threat is issued, the threatened captain will receive a power boost, a posse, and a greater chance to drop an epic rune when killed. All you have to do at this point is kill the threatened captain to get the achievement.