The Jump Helmet is a Bro Item in Mario & Luigi: Rivals in Adventure.
When using this item, Luigi puts on his head a gold shell with a trampoline on it. Mario jumps on the springboard, and the player must control Luigi with the D-Pad to allow Mario to land on the trampoline each time he comes back down. If the player presses "A" at this moment it will let Mario fly higher. After the brothers get close enough to the enemies, Mario lands on the selected baddie ("A" button command). The attack will be stronger depending on how many times Mario successfully landed on trampoline (with the "A" command), as well as how well Luigi lined up with his brother each time. The best result has Mario jumping higher than the screen for the final jump, while somersaulting for every jump.