Just rewatched that movie. Also watched the OK K. O.! Let's Be Heroes episode 'Monster Party', originally broadcast in October 2018 - exactly thirty years after Scooby-Doo and the Ghoul School was first shown. In tribute to that movie, the characters of all five featured Ghoul School pupils return for the episode. Russi Taylor (as Phantasma), Susan Blu (as Sibella), and Pat Musick (as Elsa Frankenteen) reprise their roles; Natalie Palamides and Kristen Li take over as Winnie and Tanis respectively, as Marilyn Schreffler had died and Patty Maloney had retired. Shaggy and Scooby get referenced once (obliquely), when Winnie recalls "that weird guy with the great dane".
Nice.
