After finishing a game in any game mode, you have a chance to receive a Lucky reward pop-up. 

You’ll be able to get valuable resources, such as Special Balls, Chests, Club Cards, etc. Depending on the reward, you can get it through watching a video ad, purchasing with gems, or for free.

Hurry up! Lucky rewards only last for a couple of minutes. If you miss the pop-up, they can be found in the store or on the left side of the main screen, replacing the “Free Ad Rewards” icon.