SpongeBob reads a scary book before bedtime. Because of that he sees scary creatures when he turns off the light. When at the Krusty Krab, he tells Mr. Krabs that if he blinks, he sees something scary. Mr. Krabs tells SpongeBob to get a night light so he won't be scared of the dark. However, he buys more when he finds more darkness in the house. Eventually, there are thousands of night lights in every room.
Patrick wakes up and sees SpongeBob's house lit up. He thinks SpongeBob is throwing a party and goes to his house, but SpongeBob warns him about the dark so he brings his rock inside SpongeBob's pineapple. While getting more night lights, Squidward tells them that they have too many lights and that it's just their imagination. While getting a lighthouse, it makes an M in the sky so Mermaid Man and Barnacle Boy come. Meanwhile, the Moth, one of Mermaid Man's enemies who he has been searching 57 years for, finds the light, but SpongeBob traps him inside the lighthouse, but the Moth carries the lighthouse along with the Pineapple.
SpongeBob and Patrick are alone in the dark until the sun comes up. Patrick goes up to get it, thinking it is a light and SpongeBob falls asleep. Patrick comes down again on fire shouting "Too much light!"
The original airing had Patrick saying "SpongeBob, can I sleep with you again tonight?" This was changed to "Sleepover!" in later airings, possibly because it sounded like implied homosexuality.
SpongeBob develops boogophobia, a phobia of the "boogeyman."
Double Irony: A normal child with a fear of the dark would usually sleep with only one night light. SpongeBob, out of desperation and fear, bought way too many night lights to light up the pineapple in the most impossible way, since one night light wasn't enough for him. And he wasn't able to get any sleep until the end of the episode.
Running Gag: SpongeBob getting more lights.
SpongeBob choose to bought too many night lamps, when he can just turn on all the lamps in his house.
When SpongeBob and Patrick meet Mermaid Man and Barnacle Boy they are all outside. After the shot with the letter "M", they are all in the pineapple.
The Moth looks similar to Superman, the Owlman, Mothman and even Man Ray.
When Moth lifts up SpongeBob's entire pineapple, only the very top should go since it detached from the rest of the house.
It is revealed that Squidward has a mirror on his bedroom ceiling.
The Moth is voiced by Mark Hamill, who portrays Luke Skywalker in the Star Wars films.
This is the first episode with Mermaid Man and Barnacle Boy appearing and not having their names in the title. Chronologically, the unofficial name of the episode was "Mermaid Man and Barnacle Boy VII," but the sequencing stopped after Mermaid Man and Barnacle Boy VI: The Motion Picture.
When SpongeBob looked at the bathroom being dark, if one would look closely (or possibly stand up), his pet scallop can be seen.
When the light house shines it's light through the pineapple, at first the "M" looks like it has more of a curve, but when Mermaid Man finds out the signal is a false alarm, the signal looks like a normal "M."
The episode jumps out off topic, from night light matters to a Mermaid man and Barnacle Boy conflict.
The novel SpongeBob reads breaks its fourth wall, talking about the author dying before finishing the story.
The beginning of this episode is similar to Krab Borg. SpongeBob develops fear to something after seeing something scary and keeps overreacting in both episodes.
The Big "M" signal in the sky is a reference to the Bat-Signal from Batman.
Patrick looks out his window thinking SpongeBob's having a party. However, most of Patrick's house is underground, so this is impossible and Patrick never had a window in other episodes.
When Patrick was in SpongeBob's mouth after Squidward scared them, he came out after Squidward told them it was him, but without his sleeping hat. The next shot he was seen, his hat is back on his head.
When Patrick watches SpongeBob's house, he's seeing it from an impossible angle, because Squidward's house is between them. This error also happens in The Pink Purloiner.
When SpongeBob asks Mermaid Man and Barnacle Boy if they're here to protect them from the darkness, he doesn't have any legs.