This achievement's description isn't exactly correct. Instead of an enemy you must light a large plant on fire. After obtaining the fire shuriken you must progress a bit further into the level. Eventually you will come across a very dark room where you will be ambushed. In the back right side of the room there is a large plant. Target it with your fire shuriken and *pop* goes the achievement. Pretty much needed just to progress. Even if you somehow manage to stumble through the darkness and miss this one there is another plant just down the hall on a balcony.