This bubble has similar property to the Bubble Mill in Bubble Witch 2 Saga, except the added moves are countdown from 5. The player need hit it before the countdown ends.
For example, bursting these will give you extra moves. The +3 starts with a value of 3 extra moves. However, it will deplete by one move for each turn that it’s not collected. Prioritize collecting these bubbles; they often appear in levels that start with a low move count.