Dungeon of the Mad Mage (5E)

As the party continues to explore the level, they come across what appears to be a ruined temple. Going around it, they meet a spirit on the other side. In talking with her, she states that she was a priestess and is trapped as a ghost until the Scourge that killed her have also been killed. Going further, the party eventually encounters a bone naga, which is killed after a good combat.