Nightmare is Dreams twin brother. Dream is gaurdian of positivity, and nightmare is gaurdian of negativity. Nightmare has a gang called the bad sanses, which include, killer, dust, and horror, they all worked for nightmare. Nightmare didn't care for their feelings, yet he still took care of them in his castle. Nightmare was a skeleton, like everyone else, with black goop all over him, and black goopy tendrils on his back.