The very biggest beasts of mythology are almost to huge to be seen until its too late. They are supernatural creatures that can challenge the gods, or reign supreme in the sky and unfathomed ocean depths. Meet the top ten largest and most invincible, including: Thunderbird that shot lightning form his eyes and could pick up a whale in his talons; The Midgard serpent that encircled the world; Mighty Typhon who tore up mountains; and, the sea-snake Leviathan.