Place it after the reveal line in a reaction edit, not under dialogue, then follow it with the Galaxy Brain Meme for a smug escalation, or reverse the order for a failed plan that suddenly backfires on screen.
About this sound
A 7.5-second evil laugh performed like a villain who has just figured something out, with a drawn-out cackle that builds in smug delight. It feels mischievous and triumphantly sneaky, turning a small discovery into a dramatic reveal moment that sounds pleased with itself rather than truly frightening.