Complex sentence: The China Princess also tells Dorothy that the Jester was the one responsible for making Princess Gayelette and everyone else in her kingdom disappear upon using the Wicked Witch of the West's wand where its evil took over him.
Split into simpler sentences: The China Princess also tells Dorothy that the Jester was the one responsible for making Princess Gayelette and everyone else in her kingdom disappear. When the Jester used the Wicked Witch of the West's wand it's evil took over him.