Kass is an Undead Vampire Spawn who is imprisoned in Cazador's Dungeon. She is one of the children recently kidnapped from the Gur by Astarion and forcibly turned into a vampire spawn.
As the party progresses through Cazador's Dungeon, they inevitably pass by a prison containing various children Vampire spawns, including Chessa. Like Chessa, Kass can either be consumed or set free depending on the choices made after slaying Cazador.
If Cazador is later defeated, the party can then choose to consume the souls of all vampire spawn or free them, the former resulting in Kass' immediate death. If Kass is freed, she can later be seen in the Lower City Sewers with her dad Gandrel.