Around November of 2014, when Who Killed Princess Peach was being released, StacheBros (don't ask me how) somehow inserted a brief 4-to-5-second promo for the upcoming video at the beginning every video on the channel, without affecting the upload date or anything.
It was just a quick shot of the characters followed by what would become the video's thumbnail, with a demonic voice saying "On Thursday November 6th, find out Who Killed Princess Peach", and it went away after the video came out. There aren't any archives of any of the videos in this state, and nobody's mentioned it whatsoever.