Sing Sprite

Spirit creature that has an enchanting song.
It lives under mountains and sings, the song attracts people to the mountain, and they wander into the caves to sit with the spirit and listen/join in the song.
It leads them out when it’s done singing, and the people don’t remember much; just the song.
The people feel refreshed and strangely joyous and relaxed after hearing the song.
Sometimes people don’t want to leave the creature; and the creature allows them to stay. after too much exposure people begin turning into a sing sprite, and eventually they die and their spirit is fully transformed.
Some people have been found before being fully transformed and taken out of the caves; these people seem much happier with their lives than they were before. There are other, less positive side effects, but most don’t seem to mind as they feel better about life in general.