Nightmare Sans is the emperor of the Lunar Empire, along with being the brother of Dream Sans. He is a dark melanistic skeleton with four tentacles protruding out of his back, and having what appears to be black goop running endlessly on his body exterior and interior. Nightmare is often seen as a mature, brooding, and serious figure that will usually appear to be intimidating to others. He is VERY smart and intelligent often one step ahead of most. One cyan eye(other covered in goopy substance.