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Zero is Jack Skellington's loyal pet ghost-dog from Kingdom Hearts, Kingdom Hearts II, and Kingdom Hearts 358/2 Days. He originally appeared in Tim Burton's The Nightmare Before Christmas. He also appears in Kingdom Hearts 358/2 Days alongside Jack, as well as getting a considerably expanded role in the game. However, in this game, Zero appears to be a light blue as compared to his usual white appearance.
 Kingdom Hearts
Zero had a relatively small role in Kingdom Hearts, appearing only as a ghostly hallucination.
 Kingdom Hearts 358/2 Days
 Kingdom Hearts II
Zero is a ghostly dog that appears to be made of a white sheet, much like a stereotypical ghost. Like Pluto, he has basset hound-esque floppy ears. His "eyes" are just empty holes in the sheet. Zero's snout is very long and thin, and his upper jaw curls upward at the tip. His nose is a small jack-o-lantern, and his collar is a faded brown color.
Zero first appeared in the 1993 movie The Nightmare Before Christmas. In the movie, Jack finds the door to Christmas Town while he is taking Zero for a walk. Later, when Jack wants to take off through the thick fog to deliver presents, Zero has to light the way. At the end of the movie, Jack and Sally kiss each other as Zero looks at them. He then flies into the air and transforms into a star.