Nightmare was a very evil King with Three very small and mischievous sons. Nightmare's Three children were Killer, Dust and Horror who were very messy and hyperactive. Error was Nightmare's best friend, right-hand man and most trusted ally. Error took care of the children when Nightmare couldn't and also took care of Nightmare and the chores in the castle such as cleaning, cooking, dusting...There was also a Nightmare Royal Guard; Cross. He's hatching a plan to get the throne.