Advance commands are a series of secret button presses within Bros. Attacks. These secret commands can add more power to your attacks to cause greater damage. These can be unlocked after performing a Bros. Attack a certain amount of times.
These are the andvance commands. I am missing the advance commands for Swing and Fire Bros. These secret button commands are only usable once you have unlocked them.
Splash Bros. Press A when landing on Luigi
Bounce Bros. Press A when landing on Luigi
Chopper Bros. Press A when Mario is jumping onto Luigi
Knockback Bros Press A when Mario Shrinks
Thunder Bros. Press A when Luigi Jumps onto Mario
Cyclone Bros. Press B when you move back from the opponent