The 2nd season introduces a new group of kids for The Midnight Society, dropping the cast from the previous season.
All but one of the season 1 characters were named after famous horror directors (Carpenter, Raimi, Coscarelli, and Fulci). In season 2, Hannah and Seth's last name is Romero, but they're the only ones who keep up the tradition.
Sardo and The Ghastly Grinner are some of the more infamous characters from the original series. The Ghastly Grinner only appeared in one episode (4.9: The Tale of the Ghastly Grinner) but the Ghastly Grinner comic was seen several times afterwards and was teased at the end of the 1st season of this reboot. Sardo made several appearances during the original series and the 1st reboot.