Bounce Bros. is Luigi's first Bros. Attack in the game Mario & Luigi: Superstar Saga. It is learned alongside Splash Bros. in the Stardust Fields. The move can be activated during Luigi's turn. It costs four Bros. Points (BP) in Mode 1 and Mode 2, but costs three in Mode 3.
In Bounce Bros., the move involves Luigi leaping onto Mario, who throws him into the air. When Luigi is right above him, Mario leaps into the air to grab him. The two then do a flip and Luigi slams into the enemy with his hands. The buttons that must be pressed are to let Luigi hop on Mario, to have Mario jump and catch him, and again to have them both slam down.
It takes eight uses of Bounce Bros. before learning the Advanced Command. In the advanced command, Mario and Luigi separate, each tumbling toward an enemy. The commands are to initiate the attack, to separate the Bros., again when Luigi nears the enemy he's targeting, and again when Mario nears the enemy he's targeting. If there's only one enemy, the commands are the same, but the Bros. obviously will both target that enemy.