What is Grandma hiding?

• What's Grandma hiding? is a time-limited event consisting of 5. Each step has its own treasure map goal and rewards. You can collect treasure maps by beating levels.
• When you reach the treasure map goal of a step, you get to claim your rewards for that step, then move on to the step.
• Each step has a coupon that reduces the price of Grandma's hidden box.
• The discount is maximum after completing all the steps.