Resistance 3

Leeches are essentially Grims that glow a neon green color. Shoot them in the legs and they will fall over and swell up. Now you need to wait until enemies come near the fallen leech, and shoot it to detonate it. Leeches are first introduced in Mt. Pleasent, after agreeing to go find Johnathan, in the chapter Mt. Pleasant, PA: Meet Jane Rose. Your progress towards this trophy will carry over through all playthroughs, and chapter select. It can also be farmed at checkpoints.

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, Leeches, and Leapers. Jump down in to the area and wait until the first set of Leeches to show up. Shoot one of them in the legs a few times to knock it over, and bring your large horde of Grims near the corpse. Once they are bunched up around the fallen Leech, shoot it to detonate it and kill all of the Grims around it. This will typically rack you up 4 or 5 kills. Wait a brief moment and another wave of Grims and Leeches will arrive, and you can repeat the process. After that wave, simply let the remaining enemies kill you. Your trophy progress will be saved, and all the enemies will respawn, so you can do it again.

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