Nightmare Sans is litteral nightmare. His current appearance is quite sinister. One can see the outline of Sans's shorts and hoodie. He is entirely black and goopey, with 4 tentacles coming out of his back; a side effect from the immense power of the dark apples. His left eye is constantly illuminated in battle blue. He looks like he's made out black liquid. He has sharp and creepy teeth. He's always mysterious. He's also Intelligent, and often comes up with countless schemes of darkness.