Wondering what those little faces smiling back at you from the bottom of your Collections menu are? They're keys that will unlock collections or start challenges!
How do I use keys in the game?
Green Turtle Keys unlock all collections (except Exclusive), light blue Diamond Keys unlock Exclusive series, and gold keys unlock challenges. If a key isn't green, diamond, or gold, its color corresponds to the color rarity of the collection it unlocks—for example, a white key unlocks a white collection, a red key unlocks a red collection, and so on.
You can earn keys to unlock new collections when you complete old ones (by clicking the green checkmark on your completed collections).
When you level up, you'll win Turtle Keys. These keys are unique: they can open any regular collection of any color rarity. You may also purchase a Turtle Key at any time by clicking the white shaded "Add Series" at the bottom of the Collections menu (to get there, click the Collections icon at the lower left of the play screen).