Spookwave is the 39th track in the Undertale Soundtrack. It has the same melody as Spooktune, but with a phaser/flanger effect. It is in the second CD found in Napstablook's house. The song continues playing after exiting their house. This can trigger an event where the protagonist encounters Aaron and Woshua, who are too scared to fight due to the spooky music. It consists of a single sample.
dang... that ambience...Napstablook
it's like my whole body is being spooked...
- "Spookwave" is a reference to the music genre vaporwave.