Bro Ball
Bros. Ball is a move learned by Mario and Luigi in Mario & Luigi: Partners in Time. In this move they both turn into a ball and can now move faster. Additionally, the Bros. Ball lets Mario and Luigi go under walls in the game. The move is taught by Toadsworth and Toadsworth the Younger after Yoshi's Island is cleared and before the player heads for Gritzy Desert. Later on, Mario and Luigi learn the ability to flatten Baby Mario and Baby Luigi. This move is called Baby Cakes.
In the Super Mario-Kun volumes adapted from Mario & Luigi: Partners in Time, Mario and Luigi use it as an attack rather than a utility move, where they smash into the Snoozorb in volume 35. Later, in volume 37, a four brother variation of the Bros. Ball is used against the Elder Princess Shroob.
