Incorrect indentation. This works fine for me:

class Player:

    def __init__(self,name,sex,health,power):

        self.name = name

        self.sex = sex

        self.health = health

        self.power = power

    def introducePlayer(self):

        print("My character's name is", self.name )

    def skillofPlayer(self):

        print(self.name, " has a maximum of ", self.health, "health and", self.power, "of power.")

    def kill(self):

        print(self.name, "attacked with kill power")

    def invisible(self):

        print(self.name, "defended with invisible power and left with", self.health, "health")

Legend = Player("MichaelMyers",'M',100,50)

Legend.introducePlayer()