The Arrow power-up clears the horizontal line from blocks. It also removes one layer of blockers. The exceptions are:

 - Locks

 - Hives (if there's honey around it)

 - Candles (arrow can light them up, but not remove them)

 - Boxing bags (arrow hits them once, but doesn't remove them)

 - Closed oysters

 - Bowling balls and pins

To use the Arrow, tap the Bow & Arrow button and tap the line you wish to clear.