Chain Chomp

Bow-Wow is a version of the Chain Chomp from Super Mario Bros. It is found as an enemy in A Link To The Past, as an ally in Link's Awakening, and as both an ally and enemy in Four Swords.

A Link To The Past
In A Link To The Past, Bow-Wows can be found as enemies in Turtle Rock and the Palace of the Four Sword. They are invulnerable to all forms of attack.

Link's Awakening
In Link's Awakening, Madam MeowMeow is the owner of a docile Bow-Wow. Both Bow-Wow and her owner live in Mabe Village. After completing the Tail Cave dungeon, Bow-Bow is kidnapped by a gang of Moblins. Link rescues her and brings her back to MeowMeow... who then asks him to take her pet on a walk. Bow-Wow can then be used to eat the otherwise-impenetrable Goponga Flowers blocking the entrance to the game's second dungeon, Bottle Grotto.

Although Bow-Wow can take care of most enemies for Link, she cannot be taken into dungeons.

In Link's Awakening DX, a picture can be taken with Bow-Wow.

Four Swords
Bow-wow can be obtained as a player upgrade. While Bow-wow is your 'pet' it will not attack you. It will attack enemies and other Links within it's reach. Like all items in an area, Bow-wow is not a permanent item.