Stig was brought to the Midnight Society by Tucker in season 5 after Frank's family moved away. He and Kiki already seemed to know each other, possibly they have attended the same schools or live in the same neighborhood. Possibly he might be a few years older than Tucker and could be in the same class as Kiki. Due to his lack of good hygiene and odd habits, he was strongly disliked by the other members, especially Kiki whom he seem to have attraction and feelings for, which Kiki certainly did not reciprocate. The others were except Tucker were cold and unpleasant to him for a while, but over time most of them mellowed out and begun to accept him as part of their group. Althought they still were turned off and repulsed by his odd and gross habits and mannerisms.
Stig's stories are both about outsiders judged for their appearances or tastes.