I would say Kurt Zisa because most of the other bosses don't look like something you would consider an all powerful heartless. Like parasite cage, and the pot spider thing. Those should not even be bosses. Heartless like Kurt Zisa and the phantom show a way the enemies should have been created. Big, powerfull, and cool looking. Like enough bosses like parasite cage, this is square and i know disney wants it to be more kid orientated with an image to appeal to both children and adults; but we need more bosses inspired from the final fantasy series. Just more of those huge battles against huge things.