Teresa Boo, known simply as 'Boo' in the English releases, is a recurring ghost character in the Super Mario Brothers series. Teresas are shy, spherical ghosts who cover their faces when looked at and pursue Mario and his friends when their backs are turned. Teresa Boo plays the role of an enemy and obstacle throughout various games, contributing to the spooky atmosphere in haunted stages. The character is iconic for its mischievous personality and unique movement pattern within the series.