The Soul of Night is one of the seven souls that monsters can drop after the Wall of Flesh has been killed in the world. Any enemy (excluding those summoned by statues or Meteor Heads) killed in the vicinity of 200 Ebonstone Blocks or Crimstone Blocks while in the stone layer may drop Souls of Night. Even a Corrupt enemy (such as the Corruptor) will not drop Souls of Night unless 200 or more Ebonstone Blocks are present. Enemies that do not spawn in the area, but simply followed the player there, may still drop Souls.