Which of these is not a world in the anime "Buddyfight"?

Ancient Dragon World is not a world in the anime Buddyfight. Buddyfight is a trading card game anime that features various worlds, including Dragon World, Magic World, Danger World, Dungeon World, Katana World, and Legend World. These worlds act as distinct settings where characters battle using their unique monsters and abilities. However, Ancient Dragon World does not exist in the anime, making it the correct answer to the given question.