has ADHD but doesn't have a papyrus because of his Creators of his game used his brother's code on his undyne,he seeks revenge on undyne but she is to powerful so he doesn't even care about trying to fight undyne unless he has a death wish, he doesn't like you talking about his brother since he doesn't exist, he hates some people that mention his forgotten brother, he has a  7'12 tall beast form to use when threatened, also not interested in most conversations falls Asleep if he finds it boring.