There comes a part in the game where you enter a room that has two of the regenerating egg chambers filled with red biomatter. Destroy one of them and then make your way to the other. When you get to it, it will be exposed and you'll learn that it's a failed clone of Athetos.
At this point, simply leave it alone and don't kill it. It will slowly take damage and die on its own. Once it has died on its own, the trophy will unlock.
Alternatively, you could kill it for a different trophy.