Midnight is a human child with a tan skin tone, dark brown eyes, and matching hair. They are wearing a dirty grey smock (under is a cotton moth-eaten cloak), brown pants, and black boots.
After 'Mettaton' gets to them, they dress them up in a royal outfit, which is pink and a very, very dark grey color, including a pink crown.
Depending on their actions, people can interpret Midnight as merciful or merciless. Some NPCs emphasize Midnight's kindness, understanding, and grace in the epilogue. Midnight is obedient and only will not allow others input when they follow someone else's instructions, such as when Cameronthedarksoul tells them to hide behind the conveniently-shaped lamp in the castle.
During a Genocide Route, Midnight will kill all the monsters in the Underground-ith.