Nightmare's cruel, smart, and sadistic, also it is a tall black skeleton with tentacles
Error's apathetic, quick to anger, and a bit yandere-ish. 
Horror's slightly obsessive and very food-driven, but is also a bit goofy.
Dust's regretful and solemn, but has violent outbursts- he can be quite possessive of he cares about someone.
Cross's cold and silent, with a deep sadness, but also flusters rather easily.
Killer's flirtatious, charming and confident, but struggles with old habits.