A recurring enemy from the Mario series.
Their basic appearance is of an animate, carnivorous ball and chain: a black circle or sphere with a large, toothy mouth, beady eyes, and a metal chain attached opposite the mouth. The other end of the chain is typically fixed to a sturdy, immobile object.
They behave like guard dogs, lunging at any enemy in range: their Japanese name, "Wan-wan," is an onomatopoeia for the sound a dog makes, analogous to "Woof-woof" or "Bark-bark".
They occasionally make cameo appearances in other Nintendo games. In particular, The Legend of Zelda: Link's Awakening features a friendly, domesticated Chain Chomp named BowWow which will attack Link's enemies.