Nightmare is sadistic and cruel, a ruthless skeleton monster. He is entirely black and goopy, with 4 tentacles coming out of his back. His left eye is constantly illuminated in cyan light. He eats negative feelings, for that makes him stronger. He has four tentacles coming out of his back, which he can use as extra limbs. He's immune to weapons; if stabbed, it causes no damage and he'll absorb it. He has a single soft spot for his 15 year old son, Blacklight, who he is very possessive of.