Put it just before the reveal, then follow it with Why Are You Running for the chase and a Shocked Meme Sound for the reaction, keeping the warning first so the escape and the shock follow as consequences of it.
关于此声音
This is a short spoken warning that says the red mist is coming, delivered in about one and a half seconds as a single ominous line. It lands with a tense, foreboding feeling, like a threat arriving just before something goes wrong, and it works best when the danger is still unseen.