Kill 5 enemies with friendly fire.
This trophy is missable. It requires the "Jaguar's Fear" skill, which is an automatic story unlock during the Porvenir Oil Fields. With this skill, you can craft Fear Arrows that turn enemies against each other when shot with one. The affected enemy will turn on his comrades and shoot them down, then drop dead himself.
The encounter immediately after acquiring this skill is one of the best places to achieve the trophy. Make sure you have silent arrows, cloth, and dart poison resources to craft Fear Arrows.