Susie: Susie is 19 years old. She appears to be a tall, purple, lizard-like monster with messy aubergine hair and clawed hands. She has large eyes with yellow sclera, freckles at the sides of her face, and yellow fangs. Her attire consists of a long purple cardigan, a white trimmed light blue shirt, a pair of torn jeans and a pair of black shoes.

In a Dark World (where she is right now), Susie's skin and hair colours transits to lavender pink and plum respectively. Her clothes are replaced with a long black vest with purple trims, a sleeveless purple shirt, baggy plum pants, and black boots with golden soles. She also has two black bracelets with yellow spikes on each arm, and a black belt with a large golden heart buckle.

During most of Chapter 1, Susie's eyes are hidden behind her hair, outside of certain sprites and dialogue portraits. After Kris protects her from King's attack, she uncovers them and often keeps them visible. Susie is known for being rude, vulgar, as well as making sarcastic or brutally honest remarks. She can threaten with physical violence, such as biting off someone's face. In a Dark World, she is willing to attack Darkners if they are perceived as enemies. However, Susie has a different temperament to those who are kind to her. With friends, she is expressive, willing to talk about herself, and ask for their opinions. Susie favors teasing her friends, and is more observant of their emotions. She makes an effort to be considerate, and tries to not push them to talk about a stressful issue. Susie is also loyal, readily wanting to assist a friend if they are in danger or troubled. She likes compliments, and is easily flattered. Susie also enjoys causing mischief and childish antics, such as trying to fit in a freezer. She appears to like eating in general, including non-food items (most notably chalk), and receiving gifts. She is possessive of items given to her. In susie's Dark World room, her fridge has multiple non-food items she likes, which shows that susie really enjoys eating them. Susie is implied to have self-esteem issues. She used to think that nobody liked her before she found real friends. She is also aware that she struggles academically. Susie can also occasionally project onto others. Susie seems to fall asleep easily, as evidenced by the use of the Sing command in the battle against her and Lancer, and at the end of Chapter 2, where she falls asleep almost immediately after she and Kris sit down and start watching television. Even after befriending Kris and Ralsei, Susie is still shown to very much enjoy FIGHTing. This is best shown when “defeating” the Knight, Susie say they were only getting started, and even attempts to engage with them again. Susie had a rough past, struggling to make friends, and moving away whenever she did. It was when she got to Hometown Toriel found her alone, sitting on a bench in the graveyard crying, who told her it would be okay, and got her food at the diner. Susie still resides in Hometown and attends the same class as Kris and Noelle, having arrived as a new student at some point.[4] She is close to getting expelled from School due to unknown past incidents.[5] She is universally feared among her classmates and even by Alphys, due to her appearing to be a threat. Monster Kid described her as creepily watching them and their friends playing handball. At one point, the ball rolled over to her, causing her to freeze and kick the ball as hard as possible at Undyne's car. Little else is known about Susie's history prior to the events of Deltarune.