What's Grandma Hiding? is a hidden-objects puzzle game with mystery investigation and renovation elements similar to Merge Mansion. Grandma Lucy needs the help of her granddaughter, Marie (i.e., the player), with cleaning and renovating the family's rundown mansion. Marie didn't know they had a mansion! The player uncovers clues to solve the mystery.
The game breaks down the investigation over 10 locations and 40 levels. The areas to clean, restore and investigate include the library, garden, ballroom, kitchen, basement and attic. The player can only access an area if they have enough coins to buy bus tickets and energy in the form of heart points. They also use coins to stock up on energy.
The player receives an introductory number of coins, hearts and tickets. They can also view ad videos daily to acquire more coins and collect coins and hearts as rewards at the end of each level.
At a location, the player must find specific objects noted at the bottom of the screen. If they click an object that isn't on their list, they lose an energy heart. They can track their score and energy at the lower-left corner. If they experience difficulty finding an object, they can receive a hint by viewing an advertisement.
The clues the player gathers are then handed off to another character, Chad, who helps decipher each one. They can speed up his process by viewing ads as well. They can review the clues at any time via a button on the main screen.
