Ultimate Lifeform, that's right. Quite the auspicious title for someone who couldn't be much taller than Sans, but Sans would know better than anyone that size ain't any indication of worth or skill. Or potential danger.

"Kuro a friend of yours?" says Sans, rummaging in one of his jacket pockets for something to snack on. He comes up with a packet of relish, which he tears open and squeezes into his mouth in one fluid motion.