Slugsey was a former member of the halloween monsters club. She was kind and caring to her friends, but sadly she died in the first episode of season 5 "Dead Slug". She is supposed to be a human slug and is also meant to be the dimwitted one of the group and is replaced with another dimwitted girl after her death.
Lucy and Slugsey are playing with sharp plastic toy dinosaurs and Lucy carries on saying how fun it is. After Lucy attempts to pretend that her dinosaur is flying by throwing in the air, Slugsey shouts "LUCY NO!!!", but is hit in the mouth and the sharp plastic kills her by breaking both tonsils and voicebox.