After completing the Hansel and Gretel fan "mission" press Y to enter the fan list then select Hansel and Gretel. This time it will be the same location but with a flat picture on the ground to reveal from tiles you collect. The witch will again appear right after you enlarge for the first time. Then continue to collect the tiles until you are large enough to pick up Hansel and Gretel from the beginning location, do so and the mission will end and after the conversation the cheevo will pop