The shape of the figure is quite difficult to make out in the dark, but what little Kuja and Frisk can see is... wrong, somehow. This isn't the uncanny valley, what they're dealing with is the Uncanny Mariana Trench. The effect is somewhat diminished by how the "ghost" is quite clearly quaking with fear. "Y-you swear it, kupo? You will bring no harm to me?" they stutter, accent surprisingly sophisticated. Frisk looks at Kuja from behind the creature, eyebrow arched.