The Bow-Wow is a version of the Chain Chomp from Super Mario Bros. It is found in The Legend of Zelda: A Link to the Past, The Legend of Zelda: Link's Awakening, and The Legend of Zelda: Four Swords Adventures. In Link's Awakening, Madam MeowMeow is the owner of Bow-Wow. She lives in Mabe Village and after completing the Tail Cave dungeon, Bow-Bow is kidnapped by a gang of Moblins. Link rescues him and uses him to enter the second dungeon, Bottle Grotto.
Bow-Wow eats any enemy that stands in Link's way.
There is also a picture that can be taken with Bow-Wow in Link's Awakening DX that can be printed off via the Game Boy Printer.