Agony doesn't have much of a personality, it's more in how it acts. It is emotionless, but acts rather creepy, from the way it walks (it walks similarly to Mephiles the Dark in his intro cutscene thing) to it's sudden attacks.
Agony, like all the other characters, is stronger than the average cat. Agony has a very different way of attacking, and ambushes cats when they are least expecting it.
Agony, being a robotic cat, has a steel/metal body, being grey, with slightly darker grey bolts along it's legs. It has one red ring on both of it's ears (similar to Umbreon). When not activated it's eyes are completely black, but when activated it has a small red pupil. It has red markings on it's tail, legs and forehead. When activated, all the red on Agony glows (including it's pupil). It's inner ears are the same color as the bolts on it's legs.