what am i riddle?

i am dark but i am light i fill everyone with fright i am dark but yet faceless of emotion i only come to a night to bring the fear of the unown they lock doors they scream but i am alone but i am free i love nature so calming when people try to come they start running i am different iam the same im your nightmare with no face i am nown around the world i go by many names iam told you have a circle you have an x now come to summon me you will be next can you find what i am before time runs out i am very slender i love black most times up are you ready to be next ?