his black bones and his body become a kind of black mud so much that even the clothes have merged with his body, Nightmare has tentacles that can move them as he wants, his clothes are like that of Classic!sans, a vest with a T-shirt, shorts and slippers. Nightmare is deceptive, erratic and unpredictable. He sees everyone as tools to achieve his goals and is completely devoid of empathy. He is also intelligent and often comes up with countless plans to create absolute suffering.