Puppy Alliance is a limited-time event which you can earn chests by clearing levels. Tapping on a chest will generate a piece on the map. Dragging identical pieces together will merge them into a higher-level piece. Continue merging to unlock various items in the collection and receive abundant rewards. This event is divided into 4 stages. Once all obstacles on the current map are cleared, you can use a key to unlock the next map. When switching to the next map, all pieces on the current board will be carried over to the next stage. The event ends when you have collected all pieces and rewards.

How can I participate in Puppy Alliance? 
You need to reach Level 55 to participate in Puppy Alliance.