JÃ rmungandr is a sea serpent in Norse mythology . He is the middle child of Loki and the giantess AngrboÃ a. In Norse mythology , JÃ rmungandr ( pronounced ) , mostly known as Jormungand , or JÃ rmungand , or Midgard Serpent , or World Serpent , is a sea serpent , and the middle child of the giantess AngrboÃ a and the god Loki .