Bwaluigi appears in the Lava Pits, apparently summoned by the MegaBug to stop the heroes' advance on Bowser's Castle. He is fought twice; the first time alongside his weaker ally Bwario, and the second time alongside both Bwario and the Lava Queen.
Bwaluigi behaves much like a Smasher; charging at the heroes (both on his turn and after being attacked with ranged weapons) in an attempt to hit them with the large red pipe he uses as a bludgeon. In addition to significantly more HP than most enemies (and even some bosses), he can use Magnet Dance to force characters towards him, possibly making them vulnerable to attack. He and all of his allies must be defeated to claim victory.