For this trophy you need to use your Stasis on 50 enemies. There is a good chance you will obtain this naturally as you progress through the game, but if you complete the game and still haven't gotten this you can 1. Load up a save 2. Start New Game+ or 3. Earn it during your Impossible playthrough. The easiest way to obtain this quickly is to shot the fat bloated necromorphs in the stomach and they will die and spill out little things that infect dead bodies, there are 8+ of these every time you kill one of these Bloated Necromorphs So just aim and fire you Stasis at the grouo of them on the floor and each of the little things hit by the stasis count towards the trophy. You should have this in no time if you kill the bloated necros in this way each time you encounter them!
I hope you found my guide useful!