Napstablook (/ˈnæp.stə.ˌbluːk/) is a melancholic ghost and musician who lives in Waterfall. They are encountered in the Ruins as the game's first miniboss.

Napstablook's design is that of a simple ghost, with a long white body, two eyes, and a mouth. Their sclera is black with white pupils. They have a line going down their face between their eyes.

Napstablook's name is derived from Napster, a now-defunct music sharing service, as Napstablook is often depicted with an affinity for music. It could also reference their first encounter with the protagonist, in which they are depicted pretending to sleep and blocking the path, with no way to go around them. That is—Napstablook naps to block the protagonist from progressing.