Sometimes when merging two items together, an item appears within a bubble on the merge board (often a duplicate of your new merged item). Bubble items are only available for a limited time before they disappear, leaving behind  Leaves

To get the item inside, you must break the bubble. Bubbles can be broken in the following ways:

• By watching an ad (if available)
• Spending the  Coin amount shown at the bottom of the screen, after tapping on the Bubble
• The Blocker Breaker special item (mallet)