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Six Flags Fright Fest
A commercial for the Fright Fest of Six Flags aired in 2016, with a unique placement for a screamer.
Commercial
The ad starts as a normal ad, with people enjoying the park, and a woman voiceover saying "There's something for everyone at Six Flags". However, exactly 3 seconds in, a monster clown appears and roars, before cutting to creepy imagery and a different male announcer advertising the haunted attraction for the rest of the ad.
Link
NOTE: The following video contains a screamer very early on, and you better be prepared when entering the link.
youtube.com/watch?v=H0BrPLhTjt8