Splash Bros. is a Bros. Attack in Mario & Luigi: Superstar Saga. It is one of the first two Bros. Attacks learned, the other being the Bounce Bros.. It is learned at the Stardust Fields and was used in the tutorial on how to use Bros. Attacks. The move can be activated during Mario's turn. It costs four Bros. Points in Mode 1 and Mode 2, but costs three Bros. Points in Mode 3.
In Splash Bros., the move involves Mario jumping on Luigi, throwing him in the air, then Luigi jump's under Mario, grabs him, and they both do a Spin Jump (with a huge flip at the end) to slam into the attacked enemy. The buttons that must be pressed are to have Mario jump, to have Luigi leap under him, and again to slam the enemy.
It takes twenty uses of the Splash Bros. before they can learn the Advanced Command. In the advanced command, Mario attacks the enemy solo, spinning into it. This can damage spiked foes without harm, with twice damage, but when attacking normal enemies, it will be weaker compare to the normal move. Instead of jumping up to Mario, Luigi throws him in the air again. Mario then spins very fast, drilling into the enemy. The commands are to make Mario jump, again to align Mario above Luigi, to throw Mario in the air, and again to drill into the enemy.