Place it just before the reveal in your edit, then follow it with an evil laugh once the reveal is on screen. For a slower, stranger build, start with a mysterious button sound and let this clip take over as the scene turns. That order keeps the scare clear without crowding the moment.
About this sound
This 15-second clip is a dark, atmospheric sting with no melody or spoken line, built from low, uneasy tones that hang in the air. It makes a listener feel tense and watchful, as if something strange is about to happen just out of frame. That creeping discomfort is what lets it turn an ordinary moment into something ominous in seconds.