Ansem it's a final boss in End of World.
In the game
Before defeat Ansem you can defeat the waves:
Wave 1: Welcome Party. Fodder. x 7
Wave 2: The Fat. Brute. x 3
Wave 3: Dizzy Revenge. Fodder. x 9, Roto. x 1
Wave 4: The Bonanza Bros. Spawner. x 2
Final Wave: Bad Dogs: Bulldog. x 2
After the waves has been defeated, defeat Ansem. After Ansem has been defeated, the trapped guest's cube lands and break.