The Bomb-Omb is a large group of Bomb-Omb who are led by the King Bob-omb. While travelling through Shroom City the player (of Mario Party Advance) encountered several people who mentioned the mysterious leader of the Bomb-omb Mafia was located in a secret room somewhere in Shroom City. Finding a hidden bottom floor in the mushroom condo the player found King Bob-omb and challenged him to a game of chance. Earning the respect of King Bob-omb, the player gained a mini-game and Gaddget.
The Bomb-omb Mafia supposedly protects Shroom City, but don't seem to do much when Bowser starts causing trouble.