Resistance 3

Grims are first introduced in the chapter: Haven, OK: Flooded Town. This trophy is very simple, just kill Grims, using only your grenades. This will come naturally as you play the game, since grims appear in so many places. This also carries over through chapter select, and any subsequent playthroughs. The best checkpoint to farm this trophy would be Graterford, PA: The Pit. After progressing through the pit a bit, you will pick up your cryogun. A little further down the path and you will drop in to a circular chamber that will spawn a large quantity of Grims and Leapers. Simply wait for the Grims to spawn, bunch them up, and throw a grenade in to the crowd. This will likely kill 5 or 6 at once. Another wave of Grims will rush in next and you can bunch them up and grenade them again. Now allow the remaining Leapers and Grims to kill you. Your progress will be saved, but all of the Grims will respawn and you can repeat the process.

You can track your progress towards this trophy through the Rewards tab under the Extras menu.