The Sleep Master

The Sleep Master is a characer from the thirty-second book in the Give Yourself Goosebumps series, It's Only a Nightmare!.

History
When you, the reader, and your family stay at a creepy old inn, you sleep in a creepy bed with gargoyles on the headboard. You realize that since coming to this inn, you've been having a lot of nightmares, often having to do with a strange man called "The Sleep Master." Every time you encounter him, he tells you the same message, "Wake up! Your whole life is a dream. What you call the dream world is reality. Wake up and live it!"

From there, you have to make the decision whether to try relax by either going to find a book downstairs or staying in bed to relax. This will lead to different scenarios where the you will transform into different creatures to try and escape the Sleep Master, or deal with the gargoyles on your headboard. You can also choose to face the Sleep Master, who tells you that once he was an ordinary boy until he fell asleep and became the Sleep Master. He is unable to return to the real word due to Lord Morphos. The Sleep Master tells you that you may be able to escape if you can defeat Lord Morphos.

Physical appearance
He is a blue skinned humanoid with sharp teeth. He always wears pink and purple striped pyjamas and a hat with the words "Sleep Master" or "SM" embroidered in it. He is also semi-transparent.

Trivia

 * In 2018, a contest was held for fans to submit monster designs. The winners ended up having their designs used for Madame Doom and the Sleep Master.
 * The Sleep Master is an unlockable character in Goosebumps HorrorTown.