From the Super Mario Wiki, the Mario encyclopedia
Volleybomb (known as Pass the Bob-omb in Mario & Luigi: Superstar Saga + Bowser's Minions) is a captain command in the Minion Quest: The Search for Bowser and Bowser Jr.'s Journey modes of Mario & Luigi: Superstar Saga + Bowser's Minions and Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey respectively.
In Minion Quest: The Search for Bowser, Pass the Bob-omb is the seventh captain command. It costs six CP to use. When used, the captain will pass a bomb with the opposing captain. The captain in control of the player must knock the bomb back at just the right timing with each time it heads towards them. The attack ends when one of the captains fails to time their counter correctly or after the attack has gone on long enough, damaging them.
In the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, Volleybomb goes under its current name. It can be used by Bowser Jr. when he's a Ranged type. There are modifications to it: the Minions can pass the bomb as well, while they're grouped, there is a wall separating the two teams, and the bomb will damage the entire squad. Bowser Jr.'s team will always be able to deliver the final blow whenever the attack lasts long enough, even if Volleybomb was activated by the enemy captain.