Zero

Zero is a character from all Kingdom Hearts games. He is found in Halloween Town.

He is the ghostly dog belonging to Jack Skellington. He originated from The Nightmare Before Christmas, it's most striking feature, is perhaps that his nose resembles Jack-O-Lantern, possibly a reference to his master, Jack Skellington. Zero resides in the cemetery.

Kingdom Hearts
''Jack's ghost dog. He comes out of his grave whenever Jack calls. He's very loyal to his master and loves it when Jack plays with him. He loyally followed Jack in "Tim Burton's The Nightmare Before Christmas" (1993).''

Kingdom Hearts II
''Jack's ghost dog. He comes out of his grave whenever Jack calls, and never gets tired of playing fetch with his master.''