The Vacuum Block is a key item from Mario & Luigi RPG 3. It allows Bowser to use the Vacuum command in battle.
When Bowser met Brirock, the latter was stranded on a small island off the coast of Musshība Beach. Brirock implored Bowser to rescue him, but Bowser was unmoved. Just as Bowser was about to leave, however, Brirock offered the Vacuum Block as incentive for his rescue. Seeing this, Bowser agreed to assist Brirock. Picking up a small rope that was tied to the island, Bowser dragged Brirock to shore with the help of Mario and Luigi.
The Vacuum Block allows Bowser to use the Vacuum Mushroom's power offensively. Bowser can use it to uncover the hidden Blocats during battle, and to steal various helpful items from monsters. Additionally, it can be used to inhale some entire monsters, forcing the Mario Bros. to fight them in Bowser's stomach. This last function features heavily in the final battle with Dark Bowser