When I was living in England back in the 80's there are these commercials that featured this horrifying cereal mascot. Mostly, it was kids turning into the monster whenever the cereal's name was mentioned. I just had to do a quick google to find out that this was for Sugar Puffs. Most of the commercial scared me as a kid. I was so afraid I would turn into a monster if I ate Sugar Puffs.

Sugar Puffs - Boyscouts - YouTube