Shadow Boolossus

Shadow Boolossus is Boolossus (which is 15 Boos) possessed by the Shadow Queen. Shadow Boolossus does everything the original Boolossus does, but when half of it's Bos (or 7) are sucked up, it's attack pattern changes. When it ground pounds, it creates a shockwave that destroys any Ice Elementals within the range of the shockwave. After it is defeated, Luigi receives the key to the next mansion.