Sazae-oni is a creature in Japanese folklore that is kind of like a monster or a ghost. It looks like a big snail with a human face!
According to the stories, a sazae-oni was once a human who did something really bad. They were cursed and turned into this strange monster. The sazae-oni then spends its time stalking people and trying to torment them. It can also use its giant snail shell to hide in and trick people.
But, sazae-oni aren't always bad. Sometimes they can be good and help people who are lost or in trouble. They might even offer people treasures or gifts.
Overall, sazae-oni are strange and interesting creatures that are part of Japanese mythology.