Spooktune

"Spooktune" is the 38th track that plays in the UNDERTALE Soundtrack. It is one of the 3 CDs that you can play while in Napstablook's house. The song will continue playing after you exit his house and if you were to get into an encounter while outside and with this song playing, the enemies in the encounter (Aaron and Woshua) will be too scared to fight you and will run away.

Trivia
The game data file names this song "mus_spoopy.ogg"