When Jump Bros is used, Mario will go behind Luigi and jump on top of him. The player must press A to make him jump high into the air. The player then must press B to make Luigi jump up to Mario and grab his feet. They will both flip upsidedown and land on the ground hands-first. The player has to press B to cause the bros the detach and jump over to the enemy. The player has to press A when above the enemy to grab Luigi and fall down, then press A again when landing on the enemy to do damage.
If the Wario Bros are piggybacking on the Mario Bros, the attack is different. Mario will still press A to jump up into the air, and Luigi will press B to jump up to him. However, you must press Y to grab onto Mario. They will fall to the ground, and you still press B to seperate and jump over to the enemy. You press A once again, however instead of grabbing it is moving under Luigi and Waluigi so Wario grabs them. When landing on the enemy, you press X instead of A.
If you get an "Excellent!!" on this attack 20 times, you unlock the Advanced version. Mario will still press A to jump up into the air, but instead of pressing B afterwards, press A to fall down to Luigi. When Mario is about to land on Luigi, press B to spike him up into the air. Luigi will move forwards. When Mario lands on him, press A to squish him flat. Then press B when Luigi is flat to jump high into the air WITH Mario. They will land on the enemy individually. Press A when Mario is landing, and press B when Luigi is landing to do damage.
There is also and Advanced version with the Wario Bros. You press A to jump into the air, but instead of pressing A to fall down, press X to jump off Mario and force him down. When about to land on Luigi/Waluigi, press Y to jump up and spike Mario up. When Mario lands, you still press A, then B to jump high up into the air again. When Mario, Luigi and Waluigi land, press A, then B, then Y to do damage.