You acquire the Mantis and Sorrow dolls during your fight with Screaming Mantis (you actually need to shoot them as they dangle at her sides, and then use the Mantis doll to take her down). I was hoping that I could use the Sorrow doll on the downed soldiers left after the fight, but I had no such luck.
Anyway, after you beat Mantis, beat the game. Start a New Game+ on your old save, and get to Otacon's MK.II. You will get all your gear from the previous save, including the Mantis doll. Immediately after there are 3 enemies to the left: use the Mantis doll on one of them. He will dance about in the air, and this trophy will pop.
Questions, corrections and neg vote justifications below.