King Boo, also known as the Master of Illusions, is a major antagonist in the Super Mario franchise, most notably serving as the main antagonist of the Luigi's Mansion series. sinister, clever, determined and comedic. King Boo appears as a large Boo with magenta eyes, a large indigo tongue that hangs out, wears a gold crown that has a large magenta jewel on top. He can teleport, create boos, bubbles and blue fire that he can spit out and materialize things from thin air, due to incredible power.