On some level, you'll see Loot Machines: Toy Balls come out of them, and you goal is to collect them all.

With each move, the door of a Loot Machine either opens or closes. When the door is open, the element can be hit by adjacent matches or power-ups. Each hit releases as many Toy Balls as the number of cells affected by a match or a power-up explosion.

Every collected Toy Ball counts toward the level goal. Once all the Toy Balls are collected, the Loot Machine disappears from the board.