You’ll get this one in Scarecrow Fields. As you progress through the level you’ll get to a gated area with just you and the first Mecha Imp. Just run through his legs and use your throwing knives or crossbow to take off his head. Then go back through his legs and hit the Imp who is now exposed.
Continue to progress through the level and arrive to another gated area. This time the Mecha Imp will shot something red at you. You can attempt to block it then fire or you can unload with your throwing knives or crossbow to take off his head. Go back through his legs and hit the Imp who is exposed.
Trophy popped as soon as the Mecha Imp fell and the Rune appeared. Don’t be that Gamer that gives a negative because I don’t walk you from the beginning of the stage to the point of getting the trophy. Once you understand the level you can have it completed in less than 5 minutes. Good luck!