The Treasures Of Mystery Island is an inventory-based hidden object game. Instead of searching for the objects from a list, the player has to collect the their pieces scattered about the screen. A picture of each broken object is shown at the bottom, along with the number of pieces remaining to be found. After being assembled, the objects are stored in the inventory at the right side. The player has to place the complete objects on their correct places, which usually are not in the location where they have been found.
The hint system for the Windows version is a rune stone that sits under the inventory, and replaces the cursor when picked up. The stone shines more brightly when near one of the pieces, making it shake. After being spent, the stone takes about a minute to be used again, and a green energy bar besides it fills slowly while recharging. The hint system for the Android and iOS versions is a sparkling trail that encircles the needed item. Like the Windows rune stone, it takes time to recharge after each use.
Some objects bring up a puzzle when they are put on their places. Most of them are variations of classic games like jigsaw puzzles and Simon, with a few unique ones. Some of the locations have interactive portions, where the player has to move parts or press buttons to reveal a hidden piece.
At the end of each chapter, a mini-game has to be completed on some of the previous locations. A number of objects related to one or more characters, displayed as cards on the inventory space, has to be collected (for example, toys for the boy, cutlery for the waiter, etc).