Bob-Omb Blasters is a NEW Bro Item in Mario & Luigi: Sibling Rivalry.
Wario and Waluigi simply punch the Bob-omb when it positions in front of him in perfect alignment. However, this action requires a stylus bar to perform. The player must slide on the lower screen to punch the Bob-Omb. Once it's punched, it flies towards the enemy and explode. Although it's impossible to fail this action, put it has a time limit so if you haven't punched any Bob-Omb during the action, the enemy doesn't take any damage at all.
A similar item with the same name appears in Mario & Luigi: Rivals Quest, but instead of being a Bob-Omb, it is a cannon. However, Wario and Waluigi must do the same, they have to punch the cannon and once it's punched various times, it will start shooting Bob-Ombs that will fall on all the enemies, depleting their POW, DEF or SPEED.