|Occupation||Put people to sleep|
|Age||A few hours ago|
A creature made by the Sandman to put people to sleep. Its sole purpose is to be whoever or whatever a person wants it to be in order to get them to sleep.
They have no appearance and simply appear as a transparent being, often taking the form of other people.
When the Sandman put everyone to sleep, for some reason Sophie stays awake. The Sandman creates Lullaby with the sole purpose of making her sleep. In order to accomplish it, Lullaby disguises as David Hoover and follows her around the town. It first becomes four dark shadows and torments Anne Flanagan, then becomes a group of homicidal soldiers that plan a firing squad for Regan Blumberg, and finally a dragon that sets Richard Grundler's building on fire.
Once the Unicorn reveals that the real David is asleep at his girlfriend's house, Lullaby drops the act and reveals the Sandman motives, transporting her to the Fairy World. If Sophie leaves her jewel with the Unicorn, it turns into its true form.
If Sophie decides to take the pink jewel or allows Unicorn to keep it and how she chooses to handle the Sandman, the endings may vary. If Sophie lets Unicorn keep the jewel and accidentally kills the Sandman, she gets the Bad End "Queen of the Night". Though guilt-ridden by her accidental murder, Sophie decides it was his fault for making everyone fall asleep forever. Remaining in the fairy realm, she becomes the Queen of the Night, gleefully watching the eternally slumbering world. Lullaby is forced to stay with her, and cannot vanish since Sophie is awake.
If she takes the jewel and kills the Sandman, she obtains Bad End "Sleep With One Eye Open". Upon returning home, she discovers that killing the Sandman didn't fix anything: time's still frozen, and she's the only one left awake in this eternally slumbering world. Since Sophie is forced to be awake forever, Lullaby cannot vanish. If she chooses to take the jewel and puts the Sandman to sleep, she gets Bad End "Invisible Sweet Heart". Rather than return to her miserable life, Sophie gives up her humanity so she can stay in the fairy's world, becoming a Glimmer. Lullaby is forced to stay, since they cannot vanish because Sophie is awake.
Finally, if Sophie decides to let Unicorn keep the jewel and puts the Sandman to sleep, she earns Happy End "Don't Stay Up Late at Night". Tired after chasing the Sandman and putting him to sleep, Lullaby transforms into Sophie's deceased mother and puts her to sleep. They then vanish, their work to put Sophie to sleep having been done at last.
- It's noted that Lullaby can read the Sandman's language, Sophie asks Lullaby to read notes and memento's from the Sandman.