Sebastian's body is shaped similarly to that of a sea snake, elongated with light blue scales and is Massive height. He has a extremely long Gigantic tail that is adorned with several pouches that hold the supplies that he sells to the player. At the end of his body is a large tail fin with two smaller fins above it. He has three arms, one of which is attached to his left side and is wrapped in a bloodied bandage. His hands are humanoid, but claw-like. While he only has four fingers, this is confirmed to be stylistic choice. Sebastian's face retains a humanoid appearance with fish-like features, such as an anglerfish esca on his forehead (used as a lamp when he pulls it on or off), fin-like appendages in place of ears, a fish-like mouth with teeth of a shark, and a third eye on his right side. He has black, short, wavy hair. His ear fins and claws have a black gradient. he wears a dark brown jacket with a white poet shirt under it. He also wears various belts and accessories such as a holster with a shotgun attached to a small bandolier, a portable SCRAMBLER device (So no security could find him), a wedding ring, and a small pin with a photo of a cat on it. Sebastian can be described as snarky, unpredictable, swift and violent at times. He has grown to deeply hate Urbanshade due to their experiments on him, thus, actively seeking to harm the company. He also often mock the prisoners with snarky or comedic comments about each monster after their death, indicating his indifference towards the prisoners that he meets. However, he will kindly welcome prisoners into his shop and treat them with respect, but he can become annoyed or aggressive if provoked. Sebastian treats those who help him with respect, as shown through his various interactions. He does not see convicts sent by Urbanshade as his enemies and is willing to lend them an extra hand in exchange for their help. Sebastian manages both his own makeshift shop and the Pre-Round Shop. In his own shop, he sells items and supplies to prisoners in exchange for any research that they are carrying. Sebastian unwillingly supplies items to the prisoners through Dead Drops, taking kroner in exchange for items to be left at the Submarine Dock. Sebastian is incredibly reluctant to deliver the items, gaining no benefit from the exchange and often making comments over the nearby radio about how Prisoners are lazy and ungrateful. flashing Sebastian with the Flash Beacon will cause him to grab the prisoner, warn them, and then crush the Flash Beacon before throwing them to the groun. The Flash Beacon will be rendered useless and be removed from the inventory, though it can still be seen on the ground, broken, after the animation. Flashing him again after this warning, even in subsequent runs, will make him growl in frustration before quickly grabbing a triple-barreled, sawed-off shotgun and instantly killing the prisoner. Using the Beacon Gun or The Necrobloxicon (Flash Beacon mode) yields the same result, but neither the Beacon Gun nor The Necrobloxicon is destroyed.