Berry Crushing is small mini game found within the game, being similar to that of Berry Blending found within the Hoen Region (but serving a different purpose). In order to participate in Berry Crushing, you must first obtain the Powder Jar from the man in Cerulean City. Once you have, you can connect via Wireless with other players in the Union Room in order to crush the berries they have obtained during their journey.
The key to getting most from Berry Crushing is clicking the A Button as quickly as humanly possible; this is easier done by having more players involved in the effort. The more players you have clicking the A Button as much as possible, the more powder you will receive. Certain berry combinations will also yield higher amounts of the powder you will receive from Berry Crushing.
With the powder you obtain from Berry Crushing, you can return to man in Cerulean City that gave you the Powder Jar in order to exchange said powder for healing items. He will sell the following items: Energy Powder (50 Units), Energy Root (80 Units), Heal Powder (50 Units), Revival Herb (300 Units), Protein (1000 Units), Iron (1000 Units), Carbos (1000 Units), Calcium (1000 Units), Zinc (1000 Units), HP Up (1000 Units), and PP Up (3000 Units).