Boo is a recurring character in the Mario series, known for being a ghostly antagonist. Frequently appearing in various Mario games, Boo often takes on the role of a mischievous spirit who tries to scare the protagonists. With their cute yet spooky appearance, Boos are characterized by their spherical shape, white color, and a distinctive sticking-out tongue. While they are often seen floating around, they can become shy and hide when approached. Boos play a significant role in many Mario games, including the iconic 'Mario Kart' and 'Luigi's Mansion' series, adding a layer of fun and challenge as players navigate through their ghostly antics. Their whimsical personality combines elements of fright with playfulness, making them a beloved character among fans.