Boss Brolder is a boss that appears in Super Mario 3D World as the boss of World 4-Castle: Lava Rock Lair. He is a large Brolder covered with pieces of rock and crystal of various sizes, with a large chunk of crystal acting as his nose. He has glowing yellow eyes and his arms are made of lava.
He serves as the boss of World 4. His main attack is attempting to roll into the player, much like normal Brolders. He can also spin around and scatter several flaming rocks in different directions. Later in the fight, he targets one of the players while he is spinning, slowly moving towards them. Boss Brolder also summons Brolders in the fight to assist him. If a Brolder is hit by one of Boss Brolder's attacks, they will be destroyed instantly.
Boss Brolder can only be damaged by tossing other Brolders at him. After three hits, Boss Brolder is defeated, and the Warp Box to the Goal Pole is revealed.
Boss Brolder makes a reappearance as the enemy blockade in World Castle (alongside Prince Bully), and again in World Flower-12: Boss Blitz.