Place it at the exact reveal in your edit, after the promise is on screen, then follow it with a bruh reaction for the loser and an emotional damage hit for the closing beat.
Über diesen Sound
A short 3.6-second voice clip of someone delivering the line 'sike, I lied, dunnies are mine' as a sudden reversal. It lands as playful and smug, like a prank reveal where the listener realises the offer was never real and the speaker is keeping everything for themselves.