Napstablook

 is a melancholic ghost monster and musician who lives in Waterfall. They are encountered in the Ruins as the game's first miniboss.

Personality
is a very dour individual, with low self-esteem and an introverted attitude. Despite this, they're shown to be courteous to others, such as treating the protagonist as a guest in their home, and often blaming themself and apologizing for inconveniences to be polite. Even if the protagonist previously attacked them in the Ruins on the Neutral Route, they will still treat the protagonist as a friend if the protagonist went to their house.

Neutral Route
is first found blocking the protagonist's path in the Ruins, pretending to be asleep. If the protagonist cheers them up, they will thank the protagonist for being so friendly and then leave. If the protagonist fights, they will admit that they were lowering their HP to be polite, and awkwardly leave.

If the protagonist did not fight, they'll appear in the center-bottom basement room of the Ruins' six-holed puzzle room. They will say, "I fell down a hole... now I cant get up... go on without me... wait, ghosts can fly, can't they... oh well..." They fade away afterwards, presumably to return to their house in Waterfall. (It is notable that a monster says elsewhere that it is said that only spiders and ghosts can travel in and out of the Ruins.)

does not appear again until much later when the protagonist is fighting the Mad Dummy in the Waterfall's Garbage Zone; they interrupt the fight by crying on the Dummy until they run away. apologizes for breaking up the "fun" the protagonist was having and welcomes the protagonist into their house, which is just east of Undyne's house. From this point on, wears headphones.

's house is adjacent to what is implied to be Mettaton's house, which can be unlocked with the Mystery Key sold by Bratty and Catty. In their house, you can listen to their music and they will tell you they are working on a mix CD. offers you a ghost sandwich to eat, but you are unable to eat it and phase through it. After this, suggests that the two of you lie on the floor and feel like garbage together, as this is a family tradition. If you lie down for a while, the music and background will change into relaxing space scenery.

has three playable CDs: "Spooktune", "Spookwave", and "Ghouliday". If any of the CDs are playing when you leave 's house, an event can be triggered, where Aaron and Woshua are encountered but turned off from fighting due to the frightening music. The music abruptly stops after entering the area where Undyne's house is located.

East of 's house is a snail farm owned by their family, where can also be found. used to work with their cousins at the farm before their cousins left to gain corporeal forms, making Naptsablook the last remaining worker. Here, you can play Thundersnail.

Later during Mettaton's fight, is the first viewer to call and express their gratitude for the program, saying they watch it all the time.

Genocide Route
If the protagonist has killed all of the possible monsters before their encounter, will simply fade away when the protagonist approaches. Later on, does not intervene in the Mad Dummy fight as they normally would; instead the scene ends on its own. However, the protagonist can hang out with as normal if all encounters in the area have not yet exhausted.

Endings
In the True Pacifist Route epilogue, is seen outside their house with Mettaton, having been recruited as the celebrity's sound mixer. They reveal that they were not absorbed by Asriel because when the light of Asriel knocked on their door, they just closed the blinds and continued mixing music. As a result, they initially didn't learn Frisk's name. In the credits, is seen on tour with Mettaton and Shyren.
 * White Text - "Zzzzzzzzzz"
 * Yellow Text - " Spooky DJ "
 * In order to achieve the yellow text, they have to be cheered.

In Battle

 * See Napstablook/In Battle.

Name
's name sounds like "Napster bloke". Napster is a defunct peer-to-peer file-sharing service that focused on sharing music files. This references 's computer being on a "music-sharing forum" and their general affinity for music. "Dapper Blook" is a play on the phrase "dapper bloke", which is a British phrase referring to a sharply-dressed person (usually male).

's name could also reference the protagonist's first encounter with them. In the Ruins, is found sleeping directly in the protagonist's path, with no other way around them. That is - naps to block you.

Naming the Fallen Child "Napsta" or "Blooky" will prompt the message "............ (They're powerless to stop you.)"

Trivia

 * The "Dapper Blook" top hat could be a reference to the Ghostly Gibus from Team Fortress 2.
 * Mad Dummy's fight implies 's tears feel like or are composed of acid rain.
 * , along with the Dummy, are the only enemies in Hard Mode that don't change in difficulty, due to missing a memo regarding Hard Mode.
 * By simply ignoring the light to go back to mixing their music, is the only monster whose soul wasn't taken during Asriel Dreemurr's absorption process.
 * As is a ghost, they may allude "ghost producers"; composers who sell their works to people who can then claim them as their own.
 * "Killing" will display "You lost 1 experience point" instead of EXP. This means that killing Napstablook does not ruin a Pacifist playthrough.