After uncovering the conspiracy in the Glitz Pit, you'll face Macho Grubba, the true mastermind. Grubba transforms into a powerful, muscular form. He has high HP and can deal significant damage. He also has a unique ability to 'charge up,' making his next attack even stronger. Focus your attacks when he's not charged. Yoshi's Gulp attack can be very effective, and Mario's Power Smash or Jump attacks are good choices. Guarding against his charged attacks is crucial. Keep your HP and FP high, and use your strongest Special Moves when your Star Power is full. This is a challenging fight that requires sustained offense.
