"Scary" may also be the wrong word; "tense" might be closer to the mark. In Fusion there are these sections where you'll be exploring and then suddenly your doppleganger will show up and start hunting you. It's surprising and actually pretty unnerving; you have to get away, but the thing can move basically as fast as you can and there's really not much room to maneuver. I was under the impression that the "EMI" sections in dread were basically a refinement of this, but maybe I was misinformed.