An enormous snake thousands of feet in length with jet-black scales covered in faintly-purple pulsating runes

A Giant Devouring Serpent is an enormous snake thousands of feet in length. It has jet-black and extraordinarily hard scales that are covered in faintly-purple pulsating runes. It is the scourge of cities, devouring them entirely and leaving only a featureless crater. They are extraordinarily rare; it is common for there to be not a single sighting in a century.