Slumber Princess has grayish skin and fluffy, light blue colored hair. She wears a blue colored dress, that has a cloud-like design on her chest and a dream catcher tied around the waist. She also wears a gold crown with a blue gemstone embedded into it, as well as a sleep mask that appears to function as her actual eyes according to some sprites.
Slumber Princess is one of the three canidate princesses to rule the Nameless Kingdom. However she and her sisters (the other two princesses) mysteriously disappear, causing Pillowmint Butler to send Finn and Jake to retrieve them so a ruler can be chosen. At the end of the game, Finn chooses one of them to be the ruler of the kingdom. If Slumber Princess is chosen, then the game will reveal to be a dream that BMO had.