From the Super Mario Wiki
Retrieved from "http://www.mariowiki.com/index.php?title=Mad_Boo&oldid=1987850"
Mad Boos are Boos that appear in Super Princess Peach. Mad Boos' behavior are the opposite of that of a regular Boo; Mad Boos do nothing when Princess Peach turns her back to them, but if she faces them, they will attack her. They also appear in a rarer Big Boo form called Mad Big Boo.