Kill 50 enemies while using Overdrive.

Specialist Exo soldiers are the only ones who have the ability to use Overdrive (an example would be Missions 2 and 3). The other Exo class is assault, and that does not have the Overdrive ability. To use Overdrive press [ Register or Signin to view external links. ] and you will go into a slow motion bullet time mode for a short amount of time. You can only use Overdrive while you have battery, and your battery doesn't recharge so be sure that you make every use count. You can farm the kills by simply using Overdrive and getting some kills with it, then dying or restarting your checkpoint. Your kills will carry over. You cannot check your progress towards this.

A good farming method is in the 3rd mission, "Traffic". Just when you reach the streets with civilians in the area, you will get ambushed by enemies. Use Overdrive and kill as many enemies as you can until you run out of battery. After you run out of battery, request the checkpoint and repeat until you earn this trophy. The trophy will unlock when you reach 50 kills.