Morpheus Slumber was a ghost trapped in an unmarked grave. Through sheer force of will, he was able to escape the cemetary to torture the living to death with unspeakable nightmares. He rode a ghostly green horse and was accompanied by various demons he referred to as his "nightmares." He could also physically attack people while they were asleep. After being defeated by the Duke of Darkness, Mr. Slumber was forced back into the grave.